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401. Which principle ensures that the total mechanical energy of a satellite in orbit remains constant?
ⓐ. Conservation of Linear Momentum
ⓑ. Conservation of Angular Momentum
ⓒ. Conservation of Mechanical Energy
ⓓ. Law of Inertia
Correct Answer: Conservation of Mechanical Energy
Explanation: In the absence of non-conservative forces like air resistance, the sum of kinetic and potential energies (mechanical energy) remains constant for a satellite in orbit.
402. Why does a satellite in circular orbit have constant kinetic and potential energy?
ⓐ. Because gravitational force does no work in circular motion
ⓑ. Because velocity changes continuously
ⓒ. Because the orbit is bound to Earth
ⓓ. Because mass remains constant
Correct Answer: Because gravitational force does no work in circular motion
Explanation: In circular orbit, the gravitational force acts perpendicular to the velocity, so no work is done. Thus, both kinetic and potential energy remain constant.
403. In elliptical orbits, how does the kinetic and potential energy of a satellite vary?
ⓐ. Both remain constant
ⓑ. Kinetic increases at perigee, potential increases at apogee
ⓒ. Kinetic decreases at perigee, potential decreases at apogee
ⓓ. Both vary randomly
Correct Answer: Kinetic increases at perigee, potential increases at apogee
Explanation: At perigee (closest point), the satellite moves faster, so kinetic energy is high and potential energy is more negative. At apogee, speed is lower and potential energy is less negative.
404. What happens to total mechanical energy of a satellite in elliptical orbit?
ⓐ. It changes with position
ⓑ. It is constant throughout the orbit
ⓒ. It is maximum at perigee
ⓓ. It is minimum at apogee
Correct Answer: It is constant throughout the orbit
Explanation: Although kinetic and potential energies exchange in elliptical orbit, their sum remains constant, showing conservation of mechanical energy.
405. Which of the following forces is responsible for the energy exchange between kinetic and potential energy in elliptical orbits?
ⓐ. Magnetic force
ⓑ. Gravitational force
ⓒ. Normal force
ⓓ. Centripetal pseudo force
Correct Answer: Gravitational force
Explanation: Gravitational force continuously accelerates or decelerates the satellite along its path, causing an exchange between kinetic and potential energy while keeping total energy conserved.
406. If a satellite loses mechanical energy due to atmospheric drag, what will happen to its orbit?
ⓐ. It will move to a higher orbit
ⓑ. It will spiral downward toward Earth
ⓒ. It will escape Earth
ⓓ. It will remain unaffected
Correct Answer: It will spiral downward toward Earth
Explanation: Loss of mechanical energy makes total energy more negative, decreasing orbital radius and pulling the satellite into lower orbits, eventually causing re-entry.
407. Why is the total mechanical energy of a satellite negative?
ⓐ. To indicate that the satellite is bound to Earth
ⓑ. Because kinetic energy is always zero
ⓒ. Because potential energy is always positive
ⓓ. Because energy is lost in radiation
Correct Answer: To indicate that the satellite is bound to Earth
Explanation: A negative total energy shows the satellite cannot escape Earth’s gravitational field unless it gains additional energy equal to the magnitude of binding energy.
408. What is the relation between conservation of energy and escape velocity?
ⓐ. Escape velocity is derived by equating total energy to zero
ⓑ. Escape velocity is when kinetic energy becomes zero
ⓒ. Escape velocity makes total energy more negative
ⓓ. Escape velocity is unrelated to energy
Correct Answer: Escape velocity is derived by equating total energy to zero
Explanation: At escape velocity, \(KE + U = 0\). Thus, the conservation of mechanical energy principle helps derive \(v_e = \sqrt{\tfrac{2GM}{R}}\).
409. In satellite orbits, when does the exchange between kinetic and potential energy not occur?
ⓐ. In elliptical orbit
ⓑ. In parabolic orbit
ⓒ. In circular orbit
ⓓ. In escape trajectory
Correct Answer: In circular orbit
Explanation: In circular motion, orbital speed is constant. Hence, kinetic and potential energies remain constant without exchange, though total energy is still conserved.
410. Which law of physics combines with conservation of mechanical energy to maintain stable satellite orbits?
ⓐ. Newton’s First Law
ⓑ. Newton’s Second Law
ⓒ. Newton’s Law of Gravitation
ⓓ. Archimedes’ Principle
Correct Answer: Newton’s Law of Gravitation
Explanation: Conservation of mechanical energy ensures total energy remains constant, while Newton’s law of gravitation provides the central force that maintains orbital motion.
411. What is the defining characteristic of a geostationary satellite?
ⓐ. It orbits Earth in a polar orbit
ⓑ. It always remains fixed above the same point on Earth’s equator
ⓒ. It completes one orbit in 12 hours
ⓓ. It moves faster than Earth’s rotation
Correct Answer: It always remains fixed above the same point on Earth’s equator
Explanation: A geostationary satellite has the same angular velocity as Earth’s rotation and orbits in the equatorial plane, making it appear stationary relative to a point on Earth.
412. What is the orbital period of a geostationary satellite?
ⓐ. 12 hours
ⓑ. 18 hours
ⓒ. 24 hours
ⓓ. 48 hours
Correct Answer: 24 hours
Explanation: A geostationary satellite has an orbital period equal to Earth’s rotation period (24 hours), ensuring it remains synchronized with Earth’s rotation.
413. At what altitude above Earth’s surface does a geostationary satellite orbit approximately?
ⓐ. 3600 km
ⓑ. 10,000 km
ⓒ. 35,786 km
ⓓ. 100,000 km
Correct Answer: 35,786 km
Explanation: Geostationary orbit lies at an altitude of about 35,786 km, where the orbital velocity matches Earth’s rotational angular speed.
414. Geostationary satellites are primarily used for:
ⓐ. Mineral exploration
ⓑ. Deep space communication
ⓒ. Weather forecasting and communication
ⓓ. Studying Earth’s core
Correct Answer: Weather forecasting and communication
Explanation: Because geostationary satellites stay over one location, they are ideal for telecommunications, TV broadcasting, and continuous weather monitoring.
415. Which plane must a geostationary satellite orbit in?
ⓐ. Polar plane
ⓑ. Equatorial plane
ⓒ. Inclined plane at 45°
ⓓ. Any arbitrary plane
Correct Answer: Equatorial plane
Explanation: To appear stationary relative to Earth, the satellite must orbit directly above the equator, where Earth’s rotational plane lies.
416. Which condition must hold true for a satellite to be geostationary?
ⓐ. Orbital velocity equals Earth’s escape velocity
ⓑ. Orbital angular velocity equals Earth’s rotational angular velocity
ⓒ. Orbital period equals 12 hours
ⓓ. Orbital radius is less than Earth’s radius
Correct Answer: Orbital angular velocity equals Earth’s rotational angular velocity
Explanation: For a satellite to appear stationary, its angular velocity around Earth must exactly match Earth’s angular velocity of rotation.
417. How many geostationary satellites can be placed in orbit around Earth?
ⓐ. Only one
ⓑ. About 10
ⓒ. Hundreds along the equatorial plane
ⓓ. Infinite in any orbit
Correct Answer: Hundreds along the equatorial plane
Explanation: Many satellites can share the geostationary orbit as long as they are spaced sufficiently apart to avoid interference, typically separated by degrees of longitude.
418. Why do geostationary satellites have limited coverage of Earth?
ⓐ. They cannot transmit signals globally
ⓑ. They orbit too close to Earth
ⓒ. They always remain above the equator, so polar regions are not visible
ⓓ. They move too fast to cover all regions
Correct Answer: They always remain above the equator, so polar regions are not visible
Explanation: Geostationary satellites can observe and communicate with about one-third of Earth’s surface, but high-latitude regions are poorly covered due to their position.
419. What is the main difference between geostationary and polar satellites?
ⓐ. Geostationary satellites orbit close to Earth, while polar satellites orbit far away
ⓑ. Geostationary satellites cover only one region, while polar satellites cover the entire Earth
ⓒ. Geostationary satellites move faster than polar satellites
ⓓ. Geostationary satellites are natural, while polar are artificial
Correct Answer: Geostationary satellites cover only one region, while polar satellites cover the entire Earth
Explanation: Geostationary satellites stay fixed over one area, while polar satellites sweep over the entire Earth during their orbits.
420. Which of the following is NOT a characteristic of geostationary satellites?
ⓐ. They orbit in the equatorial plane
ⓑ. They have an orbital period of 24 hours
ⓒ. They appear stationary relative to Earth
ⓓ. They orbit at low Earth orbit altitudes
Correct Answer: They orbit at low Earth orbit altitudes
Explanation: Geostationary satellites orbit in medium-to-high Earth orbit, at \~35,786 km altitude. Low Earth orbit is around a few hundred kilometers and does not allow geostationary conditions.
421. Which of the following is a major application of geostationary satellites?
ⓐ. Mapping Earth’s crust
ⓑ. Global communication and broadcasting
ⓒ. Mineral detection
ⓓ. Studying deep-space galaxies
Correct Answer: Global communication and broadcasting
Explanation: Geostationary satellites are extensively used in telecommunication, television broadcasting, and internet connectivity because they provide continuous coverage over a fixed region.
422. Why are geostationary satellites suitable for weather forecasting?
ⓐ. They orbit close to Earth and measure atmospheric pressure directly
ⓑ. They provide continuous observation of the same region
ⓒ. They change position regularly for broader coverage
ⓓ. They move over the poles to monitor global circulation
Correct Answer: They provide continuous observation of the same region
Explanation: Since they remain fixed relative to Earth, geostationary satellites can monitor cloud patterns, storms, and weather systems in real time for accurate forecasting.
423. How many geostationary satellites are typically required to cover the entire Earth’s surface (except polar regions)?
ⓐ. 2
ⓑ. 3
ⓒ. 5
ⓓ. 10
Correct Answer: 3
Explanation: Each geostationary satellite covers about one-third of Earth’s surface. Hence, 3 well-positioned satellites can provide near-global coverage, except at the poles.
424. What advantage do geostationary satellites provide for communication systems?
ⓐ. They can relay signals with minimal delay
ⓑ. They always maintain line-of-sight with fixed ground antennas
ⓒ. They consume no energy in orbit
ⓓ. They move close to the poles for maximum coverage
Correct Answer: They always maintain line-of-sight with fixed ground antennas
Explanation: Because geostationary satellites stay fixed relative to Earth, ground antennas do not need to track them, simplifying communication infrastructure.
425. Which of the following is NOT an advantage of geostationary satellites?
ⓐ. Continuous coverage of a fixed region
ⓑ. Useful for TV broadcasting and telecommunication
ⓒ. Ability to monitor a single area for long durations
ⓓ. Providing accurate coverage of polar regions
Correct Answer: Providing accurate coverage of polar regions
Explanation: Due to their equatorial position, geostationary satellites have poor visibility of high-latitude and polar regions. Polar satellites are used instead for these areas.
426. Geostationary satellites are widely used for:
ⓐ. Earthquake prediction
ⓑ. Navigation and GPS systems
ⓒ. Real-time transmission of television and radio signals
ⓓ. Deep space exploration
Correct Answer: Real-time transmission of television and radio signals
Explanation: Since these satellites stay above one region, they are highly effective in relaying continuous signals for broadcasting and telecommunications.
427. What is one major limitation of geostationary satellites despite their many advantages?
ⓐ. Short lifespan of only 1 year
ⓑ. Very high cost of placement and maintenance
ⓒ. They cannot carry imaging equipment
ⓓ. They fall back to Earth quickly
Correct Answer: Very high cost of placement and maintenance
Explanation: Launching and maintaining satellites at 35,786 km requires advanced rockets and high expenditure, which is one major limitation.
428. Why are geostationary satellites less useful for military reconnaissance?
ⓐ. They cannot take high-resolution images
ⓑ. They are too far from Earth’s surface for detailed observation
ⓒ. They constantly change position
ⓓ. They cannot detect thermal signatures
Correct Answer: They are too far from Earth’s surface for detailed observation
Explanation: At high altitudes, geostationary satellites cannot provide the same image resolution as low Earth orbit satellites, making them less suitable for reconnaissance.
429. Which communication benefit is specific to geostationary satellites compared to low Earth orbit satellites?
ⓐ. Low energy consumption for transmission
ⓑ. Reduced signal travel time
ⓒ. Stable and fixed ground antenna alignment
ⓓ. Coverage of polar regions
Correct Answer: Stable and fixed ground antenna alignment
Explanation: Since the satellite remains fixed above one region, ground antennas do not need to track its motion, unlike for low Earth orbit satellites.
430. How do geostationary satellites contribute to disaster management?
ⓐ. By predicting earthquakes
ⓑ. By providing continuous monitoring of storms, cyclones, and floods
ⓒ. By drilling into the ocean floor for data
ⓓ. By measuring volcanic gases directly
Correct Answer: By providing continuous monitoring of storms, cyclones, and floods
Explanation: Their fixed position allows continuous imaging of weather systems, helping authorities issue timely warnings for cyclones, floods, and natural disasters.
431. What is the defining characteristic of a polar satellite?
ⓐ. It orbits only above the equator
ⓑ. It passes over both poles during each orbit
ⓒ. It remains fixed above one point on Earth
ⓓ. It completes an orbit in 24 hours
Correct Answer: It passes over both poles during each orbit
Explanation: A polar satellite travels in a near north-south direction and crosses over or near Earth’s poles, allowing it to scan the entire Earth as the planet rotates beneath it.
432. What is the typical altitude range of a polar satellite?
ⓐ. 200–1000 km above Earth
ⓑ. 10,000–20,000 km above Earth
ⓒ. 35,786 km above Earth
ⓓ. 100,000 km above Earth
Correct Answer: 200–1000 km above Earth
Explanation: Polar satellites usually operate in low Earth orbit (LEO), within 200–1000 km altitude, which allows high-resolution imaging and frequent revisits.
433. How much of the Earth’s surface can a polar satellite cover over time?
ⓐ. Only equatorial regions
ⓑ. Only polar regions
ⓒ. Entire Earth’s surface
ⓓ. Only one-third of Earth’s surface
Correct Answer: Entire Earth’s surface
Explanation: Because Earth rotates under the orbital path, a polar satellite eventually covers the entire globe, making it useful for mapping and environmental monitoring.
434. Which of the following best describes the orbital period of polar satellites?
ⓐ. About 24 hours
ⓑ. About 90–100 minutes
ⓒ. About 6 hours
ⓓ. About 12 hours
Correct Answer: About 90–100 minutes
Explanation: Polar satellites in low Earth orbit complete a revolution in roughly 1.5 hours, enabling multiple passes over different parts of the Earth each day.
435. Why do polar satellites provide high-resolution images of Earth’s surface?
ⓐ. Because they orbit at a very high altitude
ⓑ. Because they orbit at low altitudes close to Earth
ⓒ. Because they remain fixed at the equator
ⓓ. Because they move slower than Earth’s rotation
Correct Answer: Because they orbit at low altitudes close to Earth
Explanation: Low altitude means they can capture detailed images, making them suitable for reconnaissance, mapping, and Earth observation.
436. Which of the following is NOT a characteristic of polar satellites?
ⓐ. They orbit in a near north-south direction
ⓑ. They cover the entire Earth’s surface over time
ⓒ. They orbit at altitudes around 200–1000 km
ⓓ. They remain fixed over one point on the equator
Correct Answer: They remain fixed over one point on the equator
Explanation: Only geostationary satellites remain fixed above one point. Polar satellites, instead, move continuously over Earth’s surface and cross over the poles.
437. Why are polar satellites ideal for Earth observation missions?
ⓐ. They only observe tropical regions
ⓑ. They cover every part of the globe over time
ⓒ. They orbit far from Earth for global coverage
ⓓ. They move synchronously with Earth’s rotation
Correct Answer: They cover every part of the globe over time
Explanation: As the Earth rotates, each successive orbit shifts westward, allowing polar satellites to image new regions on every pass, eventually covering the whole planet.
438. Which type of orbit do polar satellites generally follow?
ⓐ. Equatorial orbit
ⓑ. Inclined orbit
ⓒ. Low Earth orbit with near 90° inclination
ⓓ. High Earth orbit with 0° inclination
Correct Answer: Low Earth orbit with near 90° inclination
Explanation: Polar satellites have orbital inclinations close to 90°, ensuring they pass over or near both poles on each orbit.
439. What is one disadvantage of polar satellites compared to geostationary satellites?
ⓐ. They cannot take high-resolution images
ⓑ. They cannot cover polar regions
ⓒ. They require tracking by ground antennas due to rapid motion
ⓓ. They are placed at extremely high altitudes
Correct Answer: They require tracking by ground antennas due to rapid motion
Explanation: Because polar satellites move quickly across the sky, ground stations must constantly adjust antennas to maintain communication.
440. How often can a polar satellite pass over the same region on Earth?
ⓐ. Once every 24 hours
ⓑ. Several times a day
ⓒ. Only once per week
ⓓ. Only once per year
Correct Answer: Several times a day
Explanation: With orbital periods of about 90 minutes, polar satellites can revisit and observe the same location multiple times per day, though from slightly shifted angles.
441. Which of the following is a major application of polar satellites?
ⓐ. Real-time television broadcasting
ⓑ. Weather monitoring and forecasting
ⓒ. Deep space exploration
ⓓ. Fixed-point communication services
Correct Answer: Weather monitoring and forecasting
Explanation: Polar satellites provide global coverage and frequent passes, allowing continuous observation of weather patterns, cloud formation, and climate change, which geostationary satellites cannot do effectively.
442. Why are polar satellites suitable for environmental studies?
ⓐ. They remain fixed over one region
ⓑ. They cover the entire Earth’s surface over multiple orbits
ⓒ. They orbit far away from Earth for a broader view
ⓓ. They reflect sunlight to Earth’s atmosphere
Correct Answer: They cover the entire Earth’s surface over multiple orbits
Explanation: Since polar satellites pass over every region of the Earth, they provide global data useful for monitoring deforestation, ocean currents, glaciers, and pollution.
443. Which satellite orbit is most useful for reconnaissance and surveillance purposes?
ⓐ. Geostationary orbit
ⓑ. Polar orbit
ⓒ. Medium Earth orbit
ⓓ. High Earth orbit
Correct Answer: Polar orbit
Explanation: Polar satellites fly close to Earth and provide high-resolution images, making them highly effective for military reconnaissance, border surveillance, and disaster assessment.
444. Why are polar satellites preferred for mapping and cartography?
ⓐ. They provide repeated high-resolution images of the entire globe
ⓑ. They can hover over one location permanently
ⓒ. They transmit only communication signals
ⓓ. They operate at very high altitudes
Correct Answer: They provide repeated high-resolution images of the entire globe
Explanation: Polar satellites’ low altitude and global coverage make them ideal for mapping terrain, monitoring land-use changes, and producing accurate global maps.
445. Which of the following is an advantage of polar satellites over geostationary satellites?
ⓐ. They require no ground-based tracking
ⓑ. They provide detailed coverage of polar regions
ⓒ. They appear stationary from Earth
ⓓ. They are cheaper to launch into higher orbits
Correct Answer: They provide detailed coverage of polar regions
Explanation: Polar satellites are the only satellites that pass directly over the poles, providing essential data from high-latitude and polar regions, which geostationary satellites cannot observe well.
446. Which polar satellite application is crucial for climate change research?
ⓐ. Television signal transmission
ⓑ. Monitoring melting of glaciers and polar ice caps
ⓒ. Internet services in rural areas
ⓓ. Navigating airplanes
Correct Answer: Monitoring melting of glaciers and polar ice caps
Explanation: Polar satellites can repeatedly observe Earth’s ice-covered regions, measure ice thickness, and monitor melting trends, which are essential for climate studies.
447. Why are polar satellites effective in disaster management?
ⓐ. They provide continuous coverage of one area
ⓑ. They can capture real-time images of affected regions globally
ⓒ. They orbit at 35,786 km altitude
ⓓ. They move slower than Earth’s rotation
Correct Answer: They can capture real-time images of affected regions globally
Explanation: Polar satellites allow quick monitoring of floods, earthquakes, cyclones, and forest fires due to their multiple daily passes and global coverage.
448. Which of the following sectors benefits most from polar satellite data?
ⓐ. Agriculture and natural resource management
ⓑ. Television broadcasting
ⓒ. Banking and finance
ⓓ. Sports broadcasting
Correct Answer: Agriculture and natural resource management
Explanation: Polar satellites provide critical information on soil conditions, crop health, rainfall patterns, and water resources, supporting efficient agriculture and environmental conservation.
449. Why are polar satellites often used in Earth observation missions?
ⓐ. They remain stationary above the equator
ⓑ. They orbit close to Earth, giving high-resolution images of every region
ⓒ. They provide only partial Earth coverage
ⓓ. They orbit at very high altitudes, covering broad areas
Correct Answer: They orbit close to Earth, giving high-resolution images of every region
Explanation: Their low altitude and near-polar orbit allow them to capture detailed data from all regions, including remote and inaccessible areas.
450. Which is a significant advantage of polar satellites in global weather models?
ⓐ. They stay in fixed orbit for signal relay
ⓑ. They continuously update global atmospheric data
ⓒ. They eliminate the need for ground stations
ⓓ. They replace all communication satellites
Correct Answer: They continuously update global atmospheric data
Explanation: Polar satellites collect atmospheric temperature, humidity, and wind data worldwide, feeding into numerical weather models for accurate global forecasts.
451. What does the term “weightlessness” mean?
ⓐ. A body loses its mass in space
ⓑ. A body experiences zero gravitational force
ⓒ. A body experiences no normal reaction force
ⓓ. A body gains infinite acceleration
Correct Answer: A body experiences no normal reaction force
Explanation: Weightlessness occurs when all parts of a body are in free fall under gravity. The gravitational pull is still present, but the normal reaction (apparent weight) becomes zero, creating the sensation of being weightless.
452. Which of the following best describes the cause of weightlessness in satellites?
ⓐ. Absence of Earth’s gravitational field
ⓑ. Centrifugal force balancing gravity exactly
ⓒ. Continuous free fall of the satellite and objects inside it
ⓓ. Loss of mass in outer space
Correct Answer: Continuous free fall of the satellite and objects inside it
Explanation: Both the satellite and objects inside it fall towards Earth with the same acceleration due to gravity, so there is no relative force felt, creating weightlessness.
453. Why do astronauts inside the International Space Station (ISS) feel weightless?
ⓐ. Because they are far away from Earth’s gravity
ⓑ. Because they are in a continuous state of free fall around Earth
ⓒ. Because space has no air
ⓓ. Because their mass becomes zero in orbit
Correct Answer: Because they are in a continuous state of free fall around Earth
Explanation: The ISS is orbiting Earth in free fall. Astronauts fall along with it at the same rate, so they do not feel their weight, experiencing weightlessness.
454. Which force is absent when a person feels weightless?
ⓐ. Gravitational force
ⓑ. Centripetal force
ⓒ. Normal reaction force
ⓓ. Inertial force
Correct Answer: Normal reaction force
Explanation: The force responsible for our sensation of weight is the normal reaction from the ground. In free fall, this force is absent, leading to weightlessness.
455. If a lift falls freely under gravity, passengers inside will experience:
ⓐ. Increase in apparent weight
ⓑ. Decrease in mass
ⓒ. Weightlessness
ⓓ. Doubling of weight
Correct Answer: Weightlessness
Explanation: During free fall, both the lift and passengers accelerate equally under gravity. Since no normal force acts on the passengers, they feel weightless.
456. What is the apparent weight of a person inside a freely falling elevator?
ⓐ. Equal to real weight
ⓑ. Greater than real weight
ⓒ. Less than real weight but not zero
ⓓ. Zero
Correct Answer: Zero
Explanation: In free fall, the normal force (apparent weight) is zero, even though gravitational force still acts. Hence, the person feels completely weightless.
457. Which of the following is a misconception about weightlessness?
ⓐ. Astronauts in orbit have zero mass
ⓑ. Weightlessness is due to continuous free fall
ⓒ. Normal reaction is absent in orbit
ⓓ. Satellites and astronauts fall together under gravity
Correct Answer: Astronauts in orbit have zero mass
Explanation: Astronauts always retain their mass. They feel weightless not because their mass disappears, but because they and their spacecraft fall together under gravity.
458. Why does a diver jumping off a high diving board feel weightless momentarily?
ⓐ. Because gravity ceases to act
ⓑ. Because air resistance cancels gravity
ⓒ. Because both the diver and surroundings are in free fall
ⓓ. Because their mass becomes negligible
Correct Answer: Because both the diver and surroundings are in free fall
Explanation: While falling, the diver experiences no normal reaction from the board, leading to a brief sensation of weightlessness until hitting the water.
459. In which of the following situations will a person experience weightlessness?
ⓐ. Standing in a stationary lift
ⓑ. Standing in a lift accelerating upwards
ⓒ. Inside a satellite orbiting Earth
ⓓ. Standing on the Moon
Correct Answer: Inside a satellite orbiting Earth
Explanation: A person in orbit shares the same free fall motion as the satellite, resulting in the absence of normal force and a state of weightlessness.
460. What is the real cause of weightlessness in space travel?
ⓐ. Lack of gravity in outer space
ⓑ. Mass becoming zero in space
ⓒ. Continuous free fall of spacecraft and its occupants
ⓓ. Presence of air resistance
Correct Answer: Continuous free fall of spacecraft and its occupants
Explanation: Gravity exists everywhere, even in orbit. Weightlessness arises because the spacecraft and astronauts fall together towards Earth with the same acceleration, eliminating relative normal force.
461. Which of the following is a necessary condition for experiencing weightlessness?
ⓐ. Complete absence of gravitational force
ⓑ. Motion of the body in continuous free fall under gravity
ⓒ. Being in a vacuum chamber
ⓓ. Traveling at the speed of light
Correct Answer: Motion of the body in continuous free fall under gravity
Explanation: Weightlessness occurs when both the object and its surroundings fall freely under gravity, removing the normal reaction force that creates the sensation of weight.
462. When will a passenger in a lift feel weightless?
ⓐ. When the lift moves upward with uniform velocity
ⓑ. When the lift accelerates upward
ⓒ. When the lift accelerates downward faster than \(g\)
ⓓ. When the lift is in free fall with acceleration equal to \(g\)
Correct Answer: When the lift is in free fall with acceleration equal to \(g\)
Explanation: In free fall, the lift and passenger both accelerate downward equally, eliminating the normal reaction force, so the passenger feels weightless.
463. Which orbital condition ensures astronauts experience weightlessness?
ⓐ. The spacecraft must be beyond Earth’s gravitational field
ⓑ. The spacecraft and astronauts must both be in free fall around Earth
ⓒ. The spacecraft must orbit faster than the speed of light
ⓓ. The spacecraft must stay at rest relative to Earth
Correct Answer: The spacecraft and astronauts must both be in free fall around Earth
Explanation: Astronauts feel weightless not because gravity is absent, but because they share the same free-fall motion as the spacecraft, eliminating relative contact forces.
464. Why can a skydiver experience near weightlessness during free fall?
ⓐ. Because gravity stops acting after jumping
ⓑ. Because they are falling freely with negligible normal force acting
ⓒ. Because their mass reduces in midair
ⓓ. Because air resistance fully cancels weight
Correct Answer: Because they are falling freely with negligible normal force acting
Explanation: In free fall, the normal reaction force is absent, so the skydiver experiences weightlessness until air resistance builds up to reduce the effect.
465. What is the condition for experiencing true weightlessness inside a satellite?
ⓐ. The satellite must have zero mass
ⓑ. The satellite must accelerate upward
ⓒ. The satellite must be in continuous free fall under Earth’s gravity
ⓓ. The satellite must move in a straight line away from Earth
Correct Answer: The satellite must be in continuous free fall under Earth’s gravity
Explanation: In orbit, both the satellite and astronauts fall towards Earth at the same rate due to gravity, producing the sensation of weightlessness.
466. Which of the following will NOT produce weightlessness?
ⓐ. Standing on Earth’s surface
ⓑ. Being in a freely falling spacecraft
ⓒ. Being inside a falling lift with acceleration equal to \(g\)
ⓓ. Orbiting Earth in a satellite
Correct Answer: Standing on Earth’s surface
Explanation: On Earth, the ground provides a normal reaction force equal to one’s weight. True weightlessness only occurs in free fall when the normal force vanishes.
467. When will the apparent weight of a person become zero?
ⓐ. When only gravitational force acts without normal reaction
ⓑ. When both gravitational force and normal reaction act together
ⓒ. When upward acceleration is greater than \(g\)
ⓓ. When the body is at rest on Earth
Correct Answer: When only gravitational force acts without normal reaction
Explanation: Apparent weight is due to the normal reaction. In free fall, normal reaction disappears, so the apparent weight becomes zero even though gravity acts.
468. Why does weightlessness not require gravity to be zero?
ⓐ. Because mass becomes zero in free fall
ⓑ. Because normal reaction force becomes zero in free fall
ⓒ. Because gravitational force vanishes inside satellites
ⓓ. Because inertia cancels weight completely
Correct Answer: Because normal reaction force becomes zero in free fall
Explanation: Gravity is always present, even in orbit. Weightlessness arises because the support force (normal reaction) is absent when everything falls freely.
469. In which situation will an astronaut NOT feel weightless?
ⓐ. Inside a satellite in orbit
ⓑ. Floating inside the ISS
ⓒ. Standing on the surface of the Moon
ⓓ. In a freely falling spacecraft near Earth
Correct Answer: Standing on the surface of the Moon
Explanation: On the Moon, gravity is weaker than Earth but not absent. A normal reaction force still acts, so astronauts feel lighter, not weightless.
470. Which condition best explains why astronauts feel weightless in a spacecraft orbiting Earth?
ⓐ. The spacecraft is far away from Earth’s gravity
ⓑ. Both spacecraft and astronauts are in continuous free fall around Earth
ⓒ. The spacecraft neutralizes gravity with rockets
ⓓ. The spacecraft cancels gravity using magnetic fields
Correct Answer: Both spacecraft and astronauts are in continuous free fall around Earth
Explanation: Astronauts share the same free-fall acceleration as the spacecraft, so no normal reaction force acts on them, giving the sensation of weightlessness.
471. Which of the following is an application of weightlessness in space exploration?
ⓐ. Manufacturing large crystals in space
ⓑ. Increasing the strength of gravity
ⓒ. Reducing the speed of light
ⓓ. Increasing air pressure in rockets
Correct Answer: Manufacturing large crystals in space
Explanation: Weightlessness allows materials to mix uniformly without sedimentation. This condition is used in space labs to grow large, defect-free crystals for research and medical applications.
472. Why do astronauts train in free-fall aircraft on Earth before going to space?
ⓐ. To simulate microgravity conditions
ⓑ. To reduce their body weight permanently
ⓒ. To eliminate Earth’s gravity
ⓓ. To test rocket fuel efficiency
Correct Answer: To simulate microgravity conditions
Explanation: Aircraft flying parabolic paths create short periods of free fall, allowing astronauts to practice operating in weightlessness similar to that experienced in orbit.
473. How does weightlessness help in biological experiments aboard the ISS?
ⓐ. It eliminates the need for oxygen
ⓑ. It reveals how organisms behave without gravitational influence
ⓒ. It makes organisms massless
ⓓ. It increases Earth’s gravity
Correct Answer: It reveals how organisms behave without gravitational influence
Explanation: Scientists study how plants, microbes, and human cells adapt in microgravity, providing insights into medicine, physiology, and long-term space survival.
474. Which of the following is a practical example of weightlessness on Earth?
ⓐ. Standing on a chair
ⓑ. Falling freely inside a lift
ⓒ. Running uphill
ⓓ. Swimming in a pool
Correct Answer: Falling freely inside a lift
Explanation: In a freely falling lift, both the lift and passengers fall together at the same rate under gravity, so the passengers feel weightless.
475. Why is weightlessness useful for studying fluid behavior in space?
ⓐ. Because fluids behave the same everywhere
ⓑ. Because surface tension dominates in microgravity
ⓒ. Because fluids stop moving without gravity
ⓓ. Because fluids vanish in orbit
Correct Answer: Because surface tension dominates in microgravity
Explanation: In weightlessness, buoyancy-driven motion disappears, and fluids arrange themselves according to surface tension, allowing unique studies of fluid mechanics.
476. Which of the following best describes weightlessness in satellite orbits?
ⓐ. Satellites and objects inside are in continuous free fall together
ⓑ. Gravitational force becomes zero
ⓒ. Objects lose their mass permanently
ⓓ. Satellites remain fixed in space without motion
Correct Answer: Satellites and objects inside are in continuous free fall together
Explanation: Both satellites and their contents accelerate towards Earth at the same rate, removing normal reaction forces and creating weightlessness.
477. How does weightlessness assist in medical research in space?
ⓐ. By creating artificial gravity
ⓑ. By allowing study of bone and muscle loss
ⓒ. By eliminating the need for exercise
ⓓ. By making astronauts immune to diseases
Correct Answer: By allowing study of bone and muscle loss
Explanation: In microgravity, bones lose density and muscles weaken. Studying these effects helps scientists design treatments for osteoporosis and muscle atrophy.
478. What is the advantage of weightlessness in free-fall laboratories on Earth?
ⓐ. It increases gravitational acceleration
ⓑ. It allows researchers to replicate microgravity conditions for short periods
ⓒ. It eliminates air resistance permanently
ⓓ. It provides permanent zero gravity
Correct Answer: It allows researchers to replicate microgravity conditions for short periods
Explanation: Free-fall labs drop experimental modules from tall towers, creating several seconds of microgravity to test physics, biology, and materials experiments.
479. Why are space telescopes placed in orbit where weightlessness prevails?
ⓐ. To eliminate Earth’s atmospheric distortion
ⓑ. To make them massless
ⓒ. To reduce their lifespan
ⓓ. To increase their weight for stability
Correct Answer: To eliminate Earth’s atmospheric distortion
Explanation: Weightlessness in orbit ensures telescopes remain stable while Earth’s atmosphere no longer distorts light, enabling clear images of deep space.
480. Which of the following is a clear application of weightlessness in astronaut daily life?
ⓐ. They can walk normally like on Earth
ⓑ. They must secure themselves to eat, sleep, and work
ⓒ. They lose all gravitational pull and float into space
ⓓ. They feel lighter but still stand normally
Correct Answer: They must secure themselves to eat, sleep, and work
Explanation: In weightlessness, astronauts float freely, so they strap themselves to seats or walls during meals, sleep, or experiments to avoid drifting uncontrollably.
481. Which condition allows astronauts to conduct “zero-gravity” experiments in space stations?
ⓐ. The absence of gravitational force
ⓑ. Continuous free fall of the space station and its contents under Earth’s gravity
ⓒ. Mass reduction of astronauts in space
ⓓ. Artificial cancellation of gravity by machines
Correct Answer: Continuous free fall of the space station and its contents under Earth’s gravity
Explanation: Astronauts and their spacecraft are in orbit where they fall around Earth with the same acceleration. This removes the normal reaction force, giving a weightless environment suitable for unique experiments.
482. Which equation explains why objects inside an orbiting satellite experience weightlessness?
ⓐ. \(F = m g\)
ⓑ. \(a = \frac{F}{m}\)
ⓒ. \(g = \frac{GM}{R^2}\)
ⓓ. \(N = m(g – a)\)
Correct Answer: \(N = m(g – a)\)
Explanation: Apparent weight is due to the normal force \(N\). In free fall, acceleration \(a = g\), so \(N = m(g – g) = 0\). Hence, the apparent weight vanishes, creating weightlessness.
483. Which application of weightlessness is directly used in protein crystal growth research?
ⓐ. Proteins dissolve faster in space
ⓑ. Proteins form larger, more ordered crystals in microgravity
ⓒ. Proteins lose their structure in space
ⓓ. Proteins cannot crystallize in space
Correct Answer: Proteins form larger, more ordered crystals in microgravity
Explanation: In weightlessness, sedimentation and convection currents are absent, allowing proteins to crystallize slowly and uniformly, producing high-quality crystals for drug development.
484. Why can fuel mixing in spacecraft be studied effectively in weightlessness?
ⓐ. Because gravity enhances mixing
ⓑ. Because convection currents disappear and only molecular diffusion occurs
ⓒ. Because fuel becomes massless
ⓓ. Because chemical reactions stop in orbit
Correct Answer: Because convection currents disappear and only molecular diffusion occurs
Explanation: On Earth, fluids mix by buoyancy-driven convection. In microgravity, only diffusion dominates, allowing precise studies of fuel mixing essential for spacecraft design.
485. Which real-life phenomenon on Earth is an example of short-term weightlessness?
ⓐ. A skydiver before opening the parachute
ⓑ. A car accelerating on a highway
ⓒ. A ball rolling on a slope
ⓓ. A pendulum at its mean position
Correct Answer: A skydiver before opening the parachute
Explanation: During free fall, the skydiver experiences nearly zero normal force until air resistance becomes significant, creating a short experience of weightlessness.
486. Why is weightlessness advantageous in materials science experiments in orbit?
ⓐ. It allows testing without any gravitational interference
ⓑ. It increases the melting point of materials
ⓒ. It eliminates electrical conductivity
ⓓ. It reduces heat transfer to zero
Correct Answer: It allows testing without any gravitational interference
Explanation: Weightlessness ensures that sedimentation and buoyancy do not interfere in experiments, enabling researchers to study pure material properties like solidification and alloy formation.
487. Which equation helps explain why astronauts float inside the ISS?
ⓐ. \(F = G \frac{m_1 m_2}{r^2}\)
ⓑ. \(W = mg\)
ⓒ. \(N = m(g – a)\)
ⓓ. \(KE = \frac{1}{2}mv^2\)
Correct Answer: \(N = m(g – a)\)
Explanation: The astronauts and ISS accelerate downward with the same \(a = g\), so \(N = m(g – g) = 0\). Thus, the normal reaction force disappears, making them float.
488. How does weightlessness help in space agriculture research?
ⓐ. Plants stop growing in space
ⓑ. It allows studying plant root and shoot orientation without gravity
ⓒ. It reduces the need for water and nutrients
ⓓ. It eliminates photosynthesis
Correct Answer: It allows studying plant root and shoot orientation without gravity
Explanation: On Earth, gravity guides root growth downward (gravitropism). In microgravity, researchers can observe how plants grow and adapt without this influence, aiding future space farming.
489. Which of the following is an application of weightlessness in free-fall experiments on Earth?
ⓐ. Testing parachute deployment
ⓑ. Studying microgravity effects for a few seconds in drop towers
ⓒ. Increasing gravitational acceleration
ⓓ. Producing permanent zero gravity
Correct Answer: Studying microgravity effects for a few seconds in drop towers
Explanation: Drop towers release experimental modules in free fall, simulating weightlessness for a short time to test scientific and engineering concepts before space missions.
490. Why do astronauts need to secure liquids in sealed containers during weightlessness?
ⓐ. Because liquids evaporate instantly in orbit
ⓑ. Because without gravity, liquids form floating spheres due to surface tension
ⓒ. Because liquids lose their molecular structure
ⓓ. Because pressure forces them to vanish
Correct Answer: Because without gravity, liquids form floating spheres due to surface tension
Explanation: In microgravity, surface tension dominates liquid behavior. Liquids naturally form spheres, so astronauts use sealed containers to manage drinking water or conducting experiments safely.
491. What is the definition of the gravitational field at a point?
ⓐ. The force experienced by a unit charge at that point
ⓑ. The force experienced by a unit mass at that point
ⓒ. The acceleration produced in any body at that point
ⓓ. The energy per unit charge at that point
Correct Answer: The force experienced by a unit mass at that point
Explanation: Gravitational field is defined as the force per unit mass experienced by a test mass placed at a point. Mathematically, \(g = \frac{F}{m}\), where \(F\) is the gravitational force and \(m\) is the test mass.
492. What is the SI unit of gravitational field strength?
ⓐ. \(\text{N/C}\)
ⓑ. \(\text{J/kg}\)
ⓒ. \(\text{N/kg}\)
ⓓ. \(\text{kg/N}\)
Correct Answer: \(\text{N/kg}\)
Explanation: Gravitational field strength is force per unit mass: \(g = \frac{F}{m}\). Since force has unit Newton (N) and mass has unit kilogram (kg), the unit of \(g\) is \(\text{N/kg}\), which is dimensionally the same as \(\text{m/s}^2\).
493. Which expression represents the gravitational field due to a point mass \(M\) at a distance \(r\)?
ⓐ. \(g = \frac{GM}{r^2}\)
ⓑ. \(g = \frac{r^2}{GM}\)
ⓒ. \(g = \frac{GM}{r}\)
ⓓ. \(g = \frac{1}{GM r^2}\)
Correct Answer: \(g = \frac{GM}{r^2}\)
Explanation: A point mass \(M\) produces a gravitational field at a distance \(r\) given by \(g = \frac{GM}{r^2}\). The field decreases with the square of the distance.
494. If the gravitational field at a point is \(9.8 \,\text{N/kg}\), what does it mean?
ⓐ. A mass of 1 kg at that point experiences a force of 9.8 N
ⓑ. A charge of 1 C at that point experiences a force of 9.8 N
ⓒ. Any object moves with 9.8 m/s velocity at that point
ⓓ. The field is absent at that point
Correct Answer: A mass of 1 kg at that point experiences a force of 9.8 N
Explanation: The definition of gravitational field implies that a 1 kg mass placed at that point feels a force equal to the field strength in Newtons.
495. Inside a spherical shell of uniform mass distribution, the gravitational field is:
ⓐ. Constant and non-zero
ⓑ. Zero at the center only
ⓒ. Zero everywhere inside the shell
ⓓ. Infinity at the center
Correct Answer: Zero everywhere inside the shell
Explanation: By Newton’s shell theorem, the gravitational forces from different parts of the shell cancel out exactly inside the shell, making the net field zero everywhere inside.
496. For a uniform solid sphere of mass \(M\) and radius \(R\), what is the gravitational field at a point outside the sphere at distance \(r > R\)?
ⓐ. \(g = \frac{GM}{R^2}\)
ⓑ. \(g = \frac{GM}{r^2}\)
ⓒ. \(g = 0\)
ⓓ. \(g = \frac{GM}{r}\)
Correct Answer: \(g = \frac{GM}{r^2}\)
Explanation: Outside a solid sphere, the mass of the sphere acts as if concentrated at its center. Thus, the field is identical to that of a point mass, \(g = \frac{GM}{r^2}\).
497. At the surface of a uniform solid sphere of radius \(R\), what is the expression for gravitational field?
ⓐ. \(g = \frac{GM}{R}\)
ⓑ. \(g = \frac{GM}{R^2}\)
ⓒ. \(g = \frac{R^2}{GM}\)
ⓓ. \(g = \frac{GM}{2R^2}\)
Correct Answer: \(g = \frac{GM}{R^2}\)
Explanation: On the surface, the point is at a distance equal to the radius from the center. Substituting \(r = R\) in \(g = \frac{GM}{r^2}\), we get \(g = \frac{GM}{R^2}\).
498. For a point inside a uniform solid sphere at distance \(r < R\) from the center, the gravitational field is:
ⓐ. \(g = \frac{GM}{r^2}\)
ⓑ. \(g = \frac{GM}{R^2}\)
ⓒ. \(g = \frac{GM r}{R^3}\)
ⓓ. Zero
Correct Answer: \(g = \frac{GM r}{R^3}\)
Explanation: Inside a uniform solid sphere, only the mass enclosed within radius \(r\) contributes. Using shell theorem, \(g = \frac{GM_r}{r^2}\) where \(M_r = M \frac{r^3}{R^3}\). Substituting gives \(g = \frac{GM r}{R^3}\), which increases linearly with \(r\).
499. What is the behavior of gravitational field strength inside a uniform solid sphere?
ⓐ. Increases linearly from the center to the surface
ⓑ. Decreases linearly from the center to the surface
ⓒ. Remains constant everywhere
ⓓ. Becomes infinite at the center
Correct Answer: Increases linearly from the center to the surface
Explanation: At the center, \(g = 0\). As \(r\) increases, \(g = \frac{GM r}{R^3}\), which is directly proportional to \(r\), reaching maximum at the surface.
500. Which of the following graphs correctly represents gravitational field inside and outside a uniform solid sphere?
ⓐ. Parabolic increase inside, hyperbolic decrease outside
ⓑ. Linear increase inside, inverse square decrease outside
ⓒ. Constant inside, inverse linear outside
ⓓ. Zero everywhere
Correct Answer: Linear increase inside, inverse square decrease outside
Explanation: Inside, \(g \propto r\). Outside, \(g \propto \frac{1}{r^2}\). Thus the graph rises linearly from zero at the center, reaches maximum at the surface, and then decreases with \(1/r^2\).
This section covers Class 11 Physics MCQs – Chapter 8: Gravitation (Part 5). Based on the NCERT/CBSE syllabus, the complete set of this chapter provides 580 MCQs with detailed solutions divided into 6 structured parts. Gravitation is one of the most high-weightage topics in exams, making it vital for success in board exams and competitive exams like JEE, NEET, and state-level tests. Here in Part 5, you will practice another 100 MCQs with answers, strengthening your preparation before the final section.
- 👉 Total MCQs in this chapter: 580.
- 👉 This page contains: Fifth set of 100 solved MCQs with explanations.
- 👉 Highly useful for board exams and competitive tests.
- 👉 Use the top navigation bar to explore more chapters.
- 👉 For the last part of this series, click the Part 6 button above.