1. Laws of motion mainly connect the motion of a body with what physical cause?
ⓐ. The colour and shape of the body
ⓑ. The temperature of the surroundings only
ⓒ. The interaction called force
ⓓ. The path length already covered by the body
Correct Answer: The interaction called force
Explanation: Laws of motion explain why the state of motion of a body changes. The immediate physical cause studied in laws of motion is force, which arises from interaction between bodies. A body may be pushed, pulled, attracted by Earth, or slowed by contact with another surface. These are different examples of forces, but each can change speed, direction, or both. Colour and shape may describe the body, but they do not by themselves explain its acceleration. The main shift here is from describing motion to finding the interaction responsible for changing it.
2. A car is described as moving with speed \(20\,\text{m s}^{-1}\) along a straight road. This statement belongs most directly to
ⓐ. dynamics
ⓑ. kinematics
ⓒ. friction
ⓓ. circular motion
Correct Answer: kinematics
Explanation: Kinematics describes motion using quantities such as position, displacement, velocity, speed, and acceleration. The statement only says how fast the car is moving and gives no information about the force producing or changing that motion. Dynamics goes one step further and asks why the motion changes, usually through forces and Newton’s laws. A straight-road speed value does not automatically mean friction is being analysed. The same value \(20\,\text{m s}^{-1}\) can be used in dynamics later, but by itself it is only a description of motion.
3. A person pulls a cart using a rope. In this situation, the pull on the cart is best described as
ⓐ. a property stored permanently inside the cart
ⓑ. the distance travelled by the cart per second
ⓒ. an interaction between the rope and the cart
ⓓ. the mass of the cart converted into motion
Correct Answer: an interaction between the rope and the cart
Explanation: A force is not an isolated property of a single body in the way mass is. It appears when two bodies interact, such as a rope pulling a cart or Earth attracting a stone. The cart experiences a pull because the rope interacts with it along the direction of the rope. Speed or distance per second describes motion, not the cause of motion. The mass of the cart affects how much acceleration the force can produce, but mass itself is not the pulling interaction.
4. The symbol \(\vec{F}\) is used instead of only \(F\) when the force is being treated as
ⓐ. a vector quantity
ⓑ. a scalar quantity
ⓒ. the SI unit of mass
ⓓ. a measured time interval
Correct Answer: a vector quantity
Explanation: The arrow over \(\vec{F}\) shows that force is being treated as a vector quantity. A vector has both magnitude and direction, so two forces of the same size can produce different effects if they act in different directions. Writing only \(F\) often refers to magnitude when direction is either known or not being emphasized. The unit of force is \( \text{N} \), not \( \text{kg} \). Direction matters in laws of motion because the acceleration produced by a net force is along the direction of that net force.
5. The SI unit relation for force is completed by \(1\,\text{N}=1\,\_\_\_\_\).
ⓐ. \( \text{kg m s}^{-2} \)
ⓑ. \( \text{kg m s}^{-1} \)
ⓒ. \( \text{kg m}^{-1}\text{s}^{-2} \)
ⓓ. \( \text{kg}^{-1}\text{m s}^{-2} \)
Correct Answer: \( \text{kg m s}^{-2} \)
Explanation: The SI unit of force is newton, written as \( \text{N} \). From the relation \(F=ma\), mass has unit \( \text{kg} \) and acceleration has unit \( \text{m s}^{-2} \). Therefore the unit of force becomes \( \text{kg m s}^{-2} \). The option \( \text{kg m s}^{-1} \) is related to momentum, not force. The power \( \text{s}^{-2} \) is important because force is connected with acceleration, not just velocity.
6. Use the arrangement described below: a box is pushed \(8\,\text{N}\) east and at the same time pulled \(3\,\text{N}\) west along the same straight line. What is the net force on the box?
ⓐ. \(11\,\text{N}\) east
ⓑ. \(5\,\text{N}\) west
ⓒ. \(5\,\text{N}\) east
ⓓ. \(24\,\text{N}\) east
Correct Answer: \(5\,\text{N}\) east
Explanation: \( \textbf{Given forces:} \) \(8\,\text{N}\) east and \(3\,\text{N}\) west.
\( \textbf{Direction choice:} \) Take east as positive and west as negative.
\( \textbf{Net force relation:} \)
\[\sum F = F_{\text{east}}-F_{\text{west}}\]
\( \textbf{Substitution:} \)
\[\sum F = 8\,\text{N}-3\,\text{N}\]
\( \textbf{Calculation:} \)
\[\sum F = 5\,\text{N}\]
The positive sign means the resultant force is toward the east.
Adding \(8\,\text{N}\) and \(3\,\text{N}\) would ignore their opposite directions.
\( \textbf{Final answer:} \) The net force is \(5\,\text{N}\) east.
7. A body at rest starts moving when pushed. The most suitable description of this change is that the force has changed the body’s
ⓐ. chemical composition
ⓑ. amount of matter
ⓒ. gravitational field everywhere
ⓓ. state of motion
Correct Answer: state of motion
Explanation: A body at rest has zero velocity relative to the chosen reference frame. When a push makes it start moving, its velocity changes from zero to a non-zero value. This change in velocity means a change in state of motion. A force can produce such a change when the forces on the body are not balanced. The push does not normally change the amount of matter in the body. Laws of motion focus on the relation between force and change of motion, not on chemical change.
8. In a bicycle moving along a road, applying brakes mainly causes a change in motion because
ⓐ. braking increases the forward force
ⓑ. braking removes the bicycle’s mass
ⓒ. braking makes acceleration impossible
ⓓ. braking exerts a backward force
Correct Answer: braking exerts a backward force
Explanation: Brakes create a retarding interaction that opposes the motion of the bicycle. This force reduces the bicycle’s velocity, so the bicycle has acceleration opposite to its direction of motion. A change in speed is a change in motion and therefore belongs naturally to dynamics. The mass of the bicycle is not removed during braking. Acceleration can be negative relative to a chosen positive direction, so slowing down is still accelerated motion.
9. Match the symbols with their usual meanings in laws of motion.
| Symbol | Meaning |
|---|
| P. \(\vec{F}\) | 1. Linear momentum |
| Q. \(m\) | 2. Acceleration |
| R. \(\vec{a}\) | 3. Force |
| S. \(\vec{p}\) | 4. Mass |
The best matching is
ⓐ. P-4, Q-3, R-1, S-2
ⓑ. P-3, Q-4, R-2, S-1
ⓒ. P-3, Q-4, R-1, S-2
ⓓ. P-1, Q-2, R-3, S-4
Correct Answer: P-3, Q-4, R-2, S-1
Explanation: The symbol \(\vec{F}\) represents force, and the arrow indicates that force is a vector quantity. The symbol \(m\) represents mass, which is a scalar quantity measured in \( \text{kg} \). The symbol \(\vec{a}\) represents acceleration, the rate of change of velocity. The symbol \(\vec{p}\) represents linear momentum, which connects motion with mass through \(\vec{p}=m\vec{v}\). Distinguishing \(\vec{a}\) from \(\vec{p}\) matters because acceleration describes change of velocity, while momentum combines mass with velocity.
10. A stone falling vertically near Earth changes its speed mainly because
ⓐ. its mass becomes zero while falling
ⓑ. time acts upward on the stone
ⓒ. velocity is always directed downward for every body
ⓓ. Earth exerts a gravitational force on it
Correct Answer: Earth exerts a gravitational force on it
Explanation: A falling stone is acted upon by Earth’s gravitational force. This force is directed vertically downward and changes the stone’s velocity. The stone’s mass does not become zero during the fall; mass is a property of the body. Time is not a force and cannot act upward or downward. The direction of velocity depends on the motion, but the cause of the changing velocity in this case is the gravitational interaction with Earth.
11. Study the table and identify the row that best separates kinematics from dynamics.
| Row | Kinematics | Dynamics |
|---|
| P | Describes motion | Explains motion using forces |
| Q | Explains forces | Ignores acceleration |
| R | Deals only with rest | Deals only with circular motion |
| S | Uses only mass | Uses only time |
ⓐ. Row Q
ⓑ. Row P
ⓒ. Row R
ⓓ. Row S
Correct Answer: Row P
Explanation: Kinematics describes motion using quantities such as displacement, velocity, and acceleration. It does not ask what interaction produced that motion. Dynamics studies the causes of motion and relates force to the change in motion. Row P captures this difference without excluding any valid kind of motion. Dynamics does not ignore acceleration; acceleration is central to Newton’s second law. A clean separation is that kinematics describes the motion, while dynamics explains the motion through forces.
12. A force of \(1\,\text{N}\) acting on a mass of \(1\,\text{kg}\) produces what acceleration when no other force acts?
ⓐ. \(1\,\text{m s}^{-1}\)
ⓑ. \(1\,\text{kg m s}^{-1}\)
ⓒ. \(1\,\text{kg m}^{-2}\text{s}^{-2}\)
ⓓ. \(1\,\text{m s}^{-2}\)
Correct Answer: \(1\,\text{m s}^{-2}\)
Explanation: \( \textbf{Given:} \) Force \(F=1\,\text{N}\) and mass \(m=1\,\text{kg}\).
\( \textbf{Required:} \) Acceleration \(a\).
\( \textbf{Unit relation:} \)
\[1\,\text{N}=1\,\text{kg m s}^{-2}\]
\( \textbf{Newton’s second-law form:} \)
\[F=ma\]
\( \textbf{Rearranging:} \)
\[a=\frac{F}{m}\]
\( \textbf{Substitution:} \)
\[a=\frac{1\,\text{N}}{1\,\text{kg}}\]
\( \textbf{Using the newton definition:} \)
\[a=\frac{1\,\text{kg m s}^{-2}}{1\,\text{kg}}=1\,\text{m s}^{-2}\]
The unit \( \text{m s}^{-1} \) would describe velocity, not acceleration.
\( \textbf{Final answer:} \) The acceleration is \(1\,\text{m s}^{-2}\).
13. A force is completely specified only when its magnitude is given along with
ⓐ. its colour
ⓑ. the name of the observer
ⓒ. its direction of action
ⓓ. the temperature of the object
Correct Answer: its direction of action
Explanation: Force is a vector quantity, so magnitude alone is not enough to describe it completely. A force of \(10\,\text{N}\) east and a force of \(10\,\text{N}\) west have the same magnitude but different effects on the body. The direction decides how the force combines with other forces and what acceleration it tends to produce. Colour and temperature may be physical properties in other contexts, but they do not complete the description of a force vector. This is why symbols such as \(\vec{F}\) are useful when direction is important.
14. A block is pulled to the right by \(6\,\text{N}\) and pushed to the right by another \(4\,\text{N}\). With no other horizontal force, the resultant horizontal force is
ⓐ. \(2\,\text{N}\) right
ⓑ. \(10\,\text{N}\) right
ⓒ. \(10\,\text{N}\) left
ⓓ. \(24\,\text{N}\) right
Correct Answer: \(10\,\text{N}\) right
Explanation: \( \textbf{Given horizontal forces:} \) \(6\,\text{N}\) right and \(4\,\text{N}\) right.
\( \textbf{Direction check:} \) Both forces act along the same line and in the same direction.
\( \textbf{Resultant relation:} \)
\[\sum F = 6\,\text{N}+4\,\text{N}\]
\( \textbf{Calculation:} \)
\[\sum F = 10\,\text{N}\]
The direction remains to the right because both contributing forces point right.
Subtracting the forces would be suitable only if they acted in opposite directions.
Multiplying \(6\) and \(4\) has no meaning for finding the resultant of two collinear forces.
\( \textbf{Final answer:} \) The resultant horizontal force is \(10\,\text{N}\) right.
15. Two descriptions are given below.
I. A ball changes its direction while moving around a curve.
II. A cart speeds up when pulled forward.
What do both descriptions have in common?
ⓐ. Both require the mass of the object to become zero
ⓑ. Both describe motion without any possible force
ⓒ. Both involve a change in the state of motion
ⓓ. Both prove that direction is not important in mechanics
Correct Answer: Both involve a change in the state of motion
Explanation: A change in the state of motion can mean a change in speed, a change in direction, or both. In statement I, the direction of velocity changes as the ball moves around a curve. In statement II, the speed changes as the cart speeds up. Both changes require attention to dynamics when the cause is being studied. The mass of the object need not become zero in either case. Direction is especially important in mechanics because velocity, acceleration, and force are vector quantities.
16. A reference frame is needed in describing motion because
ⓐ. force loses its direction in any frame
ⓑ. motion is relative to a frame
ⓒ. mass changes its SI unit between frames
ⓓ. time cannot be measured in mechanics
Correct Answer: motion is relative to a frame
Explanation: Motion is described relative to a chosen reference frame. A passenger sitting inside a moving bus is at rest relative to the bus but moving relative to the ground. The description of velocity and acceleration must therefore mention or imply a frame of reference. Force remains a vector quantity and does not lose its direction because a frame is chosen. The SI unit of mass remains \( \text{kg} \), so the role of the frame is about describing motion, not changing basic units.
17. In the early study of laws of motion, mass is introduced as a quantity connected with
ⓐ. brightness of the body
ⓑ. direction of velocity only
ⓒ. time taken by a clock
ⓓ. inertia of the body
Correct Answer: inertia of the body
Explanation: Mass is closely related to inertia, which is the resistance of a body to change in its state of motion. A body with greater mass is harder to start, stop, or deflect by the same applied force. This does not mean mass is a force; rather, it measures how strongly a body resists acceleration. Brightness and clock time do not measure this resistance. This link between mass and inertia prepares the meaning of Newton’s laws without confusing mass with weight.
18. A heavy trolley and a light trolley are initially at rest on a smooth horizontal floor. The same horizontal force acts on each for the same short time. The lighter trolley is expected to
ⓐ. remain exactly at rest because it is lighter
ⓑ. have greater inertia than the heavy trolley
ⓒ. show a larger change in motion
ⓓ. experience no force because the floor is smooth
Correct Answer: show a larger change in motion
Explanation: For the same applied force, a smaller mass offers less resistance to change in motion. The lighter trolley therefore gains acceleration more easily than the heavier trolley. Smoothness of the floor only suggests that friction may be small; it does not remove the applied force. The heavier trolley has greater inertia because inertia increases with mass. The comparison is not about which trolley has a force acting on it, but about how much its motion changes under the same force.
19. Forces are listed below.
| Case | Description | Type of interaction |
|---|
| P | A hand pushes a door | Contact interaction |
| Q | Earth pulls a falling stone | Non-contact interaction |
| R | A string pulls a small block | Contact interaction through the string |
| S | A magnet attracts an iron pin | Non-contact interaction |
Which case pairs are classified suitably?
ⓐ. P, Q, R, S
ⓑ. P and Q only
ⓒ. Q and S only
ⓓ. P and R only
Correct Answer: P, Q, R, S
Explanation: A push by a hand on a door is a contact force because the bodies touch. A string pulling a block is also treated as a contact interaction transmitted through the string. Earth’s gravitational pull on a stone does not require contact, so it is a non-contact interaction. A magnet can attract an iron pin without touching it, so it is also a non-contact interaction. The important separation is not whether the force is visible, but whether physical contact is needed for that interaction.
20. A notebook says that weight is “the force with which Earth attracts a body.” The best unit for this quantity is
ⓐ. \( \text{kg} \)
ⓑ. \( \text{m s}^{-1} \)
ⓒ. \( \text{s} \)
ⓓ. \( \text{N} \)
Correct Answer: \( \text{N} \)
Explanation: Weight is a force, so its SI unit is the newton, \( \text{N} \). Mass is measured in \( \text{kg} \), but weight is not the same quantity as mass. Near Earth, the magnitude of weight is commonly written as \(W=mg\), where \(m\) is mass and \(g\) is acceleration due to gravity. Since \(m\) has unit \( \text{kg} \) and \(g\) has unit \( \text{m s}^{-2} \), the product has unit \( \text{kg m s}^{-2}=\text{N} \). The unit \( \text{m s}^{-1} \) belongs to velocity, while \( \text{s} \) belongs to time.
