1
A student observes a boat moving forward when the canoeist pushes water backwards with a paddle. The student wonders why the boat moves forward when the paddle pushes backward. Explain this phenomenon using Newton's third law of motion. 3marks
2
An object is moving with a constant velocity. Which of the following statements must be true about the net force acting on the object?(a) The net force is zero.(b) The net force is in the direction of motion.(c) The net force is opposite to the direction of motion.(d) The net force is non-zero but zero in magnitude.1mark
3
A heavy box is pushed along a horizontal floor with a constant force. If the box is moving with constant velocity, what can be said about the force of friction?(a) The force of friction is zero.(b) The force of friction is equal in magnitude and opposite in direction to the applied force.(c) The force of friction is less than the applied force.(d) The force of friction is greater than the applied force.1mark
4
Assertion: When you jump from a height, you tend to get hurt more on a hard surface than on a soft surface.Reason: A soft surface increases the time of impact, thus decreasing the force experienced.(a) Both assertion and reason are true and reason is the correct explanation of assertion.(b) Both assertion and reason are true but reason is not the correct explanation of assertion.(c) Assertion is true but reason is false.(d) Both assertion and reason are false.1mark
5
A car is moving at a constant speed in a straight line. Suddenly, the driver applies the brakes.(i) What happens to the net force acting on the car?(ii) What happens to the velocity of the car?2marks
6
A group of students is playing tug-of-war. Team A pulls the rope with a force of 800 N, and Team B pulls with a force of 750 N in the opposite direction.(i) Calculate the net force acting on the rope.(ii) In which direction will the rope move?3marks
7
Case Study: A cyclist is riding a bicycle on a straight road. At one point, they stop pedalling and observe that the bicycle gradually slows down and stops after travelling some distance.(i) What force is primarily responsible for slowing down the bicycle?(ii) Explain why this force causes the bicycle to slow down, referencing Newton's laws of motion.(iii) If the road were frictionless, what would happen to the bicycle once the cyclist stopped pedalling?5marks
8
A book is resting on a table. A student pushes the book horizontally with a force of 5 N, but the book does not move.(i) What is the magnitude of the force of friction acting on the book?(ii) What is the net force acting on the book?2marks
9
Assertion: Newton's first law of motion is also called the law of inertia.Reason: Inertia is the tendency of an object to resist any change in its state of rest or uniform motion.(a) Both assertion and reason are true and reason is the correct explanation of assertion.(b) Both assertion and reason are true but reason is not the correct explanation of assertion.(c) Assertion is true but reason is false.(d) Both assertion and reason are false.1mark
10
A rocket engine expels hot gases downwards at a very high speed. Explain how this causes the rocket to move upwards, using Newton's third law of motion. 3marks
11
Situational Analysis: A spacecraft is moving in deep space, far from any significant gravitational sources. It is currently moving at a constant velocity.(i) What is the net force acting on the spacecraft?(ii) If the spacecraft needs to change its velocity (either speed or direction), what must it do? Explain why.3marks
12
A ball is dropped from a height and it falls towards the ground.(i) What is the force acting on the ball?(ii) If the ball has a mass of 0.5 kg, calculate the acceleration of the ball assuming .3marks
13
Data Interpretation: The velocity-time graph of a car is shown below. The mass of the car is 1200 kg.
[Graph Description: A velocity-time graph where velocity is on the y-axis (in m/s) and time is on the x-axis (in s). The graph shows three segments:
1
From 0 s to 5 s, velocity increases linearly from 0 m/s to 10 m/s.
2
From 5 s to 10 s, velocity remains constant at 10 m/s.
3
From 10 s to 15 s, velocity decreases linearly from 10 m/s to 0 m/s.]
Calculate the force acting on the car during:
(i) the first 5 seconds.
(ii) the interval from 5 seconds to 10 seconds.
(iii) the last 5 seconds.
[5 marks]
14
Assertion: When you push a wall, the wall pushes you back with an equal and opposite force.Reason: Forces always occur in pairs.(a) Both assertion and reason are true and reason is the correct explanation of assertion.(b) Both assertion and reason are true but reason is not the correct explanation of assertion.(c) Assertion is true but reason is false.(d) Both assertion and reason are false.1mark
15
A block of mass 10 kg is placed on a rough horizontal surface. A force of 60 N is applied horizontally to the block, but it does not move.(i) What is the force of friction acting on the block?(ii) What is the net force acting on the block?2marks
16
Application: When catching a fast-moving cricket ball, a fielder moves their hands backward. Explain the physics behind this action, relating it to Newton's second law. 3marks
17
Two forces, 15 N and 10 N, are applied to an object of mass 2 kg.(i) If both forces act in the same direction, calculate the acceleration of the object.(ii) If the forces act in opposite directions, calculate the acceleration of the object.3marks
18
Case Study: An athlete is preparing for a long jump. They run at a high speed before jumping.(i) Why does the athlete run before jumping? Explain using Newton's laws.(ii) When the athlete lands, they try to roll forward. Why is this beneficial?5marks
19
A student observes that a light object and a heavy object, when dropped from the same height, reach the ground at approximately the same time, even though the heavier object has a larger gravitational force acting on it. Explain this observation using Newton's second law of motion. 3marks
20
Assertion: A car moving with constant velocity on a straight road experiences zero net force.Reason: According to Newton's first law, an object continues in its state of rest or uniform motion unless acted upon by a net external force.(a) Both assertion and reason are true and reason is the correct explanation of assertion.(b) Both assertion and reason are true but reason is not the correct explanation of assertion.(c) Assertion is true but reason is false.(d) Both assertion and reason are false.1mark
Answers
1
This phenomenon is explained by Newton's third law of motion. For every action, there is an equal and opposite reaction. When the canoeist pushes the water backward (action), the water pushes the paddle and hence the boat forward with an equal and opposite force (reaction).
2
(a) The net force is zero.
3
(b) The force of friction is equal in magnitude and opposite in direction to the applied force.
4
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
5
(i) The net force acting on the car will be in the direction opposite to its motion (due to braking).(ii) The velocity of the car will decrease.
6
(i) Net force = 800 N - 750 N = 50 N.(ii) The rope will move in the direction of Team A (the direction of the larger force).
7
(i) The primary force responsible for slowing down the bicycle is the force of friction (between the tires and the road, and air resistance).(ii) According to Newton's first law, an object in motion continues in motion with constant velocity unless acted upon by a net external force. The force of friction acts opposite to the direction of motion, creating a net force that opposes the motion. This net force causes the bicycle to decelerate (change its velocity), eventually coming to rest.(iii) If the road were frictionless, there would be no force opposing the motion. According to Newton's first law, the bicycle would continue to move with the same constant velocity indefinitely.
8
(i) Since the book does not move, the applied force is balanced by the force of friction. Therefore, the force of friction is 5 N.(ii) The net force acting on the book is zero because the forces are balanced.
9
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
10
This is an application of Newton's third law of motion. The rocket engine expels hot gases downwards (action). In reaction, the gases exert an equal and opposite force upwards on the rocket. This upward force is what propels the rocket into the air.
11
(i) The net force acting on the spacecraft is zero because it is moving with constant velocity.(ii) To change its velocity, the spacecraft must exert a force in the opposite direction of the desired change in velocity (e.g., by firing thrusters). This is because, according to Newton's second law, a net force is required to produce acceleration (a change in velocity). By expelling mass (like burning fuel), it exerts a force on the expelled mass, and by Newton's third law, the expelled mass exerts an equal and opposite force on the spacecraft, changing its velocity.
12
(i) The force acting on the ball is the gravitational force (weight) exerted by the Earth.(ii) Acceleration () can be calculated using Newton's second law, . Here, . So, .Therefore, the acceleration of the ball is .
13
First, calculate the acceleration in each interval.(i) Interval 0 s to 5 s: , , ..Force (acting in the direction of motion).(ii) Interval 5 s to 10 s: Velocity is constant (), so acceleration .Force .(iii) Interval 10 s to 15 s: , , ..Force (acting opposite to the direction of motion).
14
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
15
(i) Since the block does not move, the applied force is balanced by the force of friction. Therefore, the force of friction is 60 N.(ii) The net force acting on the block is zero because the forces are balanced.
16
When catching a fast-moving cricket ball, the fielder moves their hands backward. This action increases the time interval over which the ball's momentum changes from its initial high value to zero. According to Newton's second law (in its momentum form, ), if the change in momentum () is the same, increasing the time interval () decreases the magnitude of the force () experienced by the fielder, thus minimizing injury.
17
(i) Net force = 15 N + 10 N = 25 N.Acceleration .(ii) Net force = 15 N - 10 N = 5 N.Acceleration .
18
(i) The athlete runs before jumping to gain momentum. According to Newton's first law, an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force. By running, the athlete increases their mass-in-motion (momentum), which helps them to jump further. Newton's second law also implies that with more initial momentum, it's possible to achieve a greater impulse and thus a greater change in velocity (the jump).(ii) When landing, rolling forward increases the time of impact with the ground. According to Newton's second law (), by increasing the time () over which the change in momentum () occurs, the force () experienced by the athlete is reduced, preventing injury.
19
While the gravitational force on the heavier object is larger, its mass is also larger. According to Newton's second law (), the acceleration of an object is directly proportional to the net force and inversely proportional to its mass. Since the force is the weight (), the acceleration due to gravity is . Therefore, the acceleration due to gravity is independent of the mass of the object, and both objects fall with the same acceleration, reaching the ground at approximately the same time (ignoring air resistance).
20
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
