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# Form 3 Physics Newton's laws of motion questions and answers

This online session contains Form 3 Physics Newton's Laws of Motion questions and answers. The questions are well explained with video solutions.

Lessons (**44**)

- 1.
State Newton’s first law of motion.

2m 6s - 2.
A trolley is moving at constant speed in friction compensated track. Some plasticine is dropped on the trolley and sticks on it. State
with a reason what is observed about the motion of the trolley.

2m 14s - 3.
A gun is fired vertically upwards from the top of an open truck moving horizontally at a uniform velocity of 50 ms-1. The bullet achieves a maximum
height of 45m.
(i) State with reason whether or not the bullet will land on the truck.
(ii) Calculate the distance covered by the truck just before the bullet reaches the level from which it was fired. (Use g=10 #ms^-2#).

7m 26s - 4.
An industrial trolley of mass 20kg carrying a mass of 50kg is acted on by a constant force. The trolley moves along a horizontal smooth
surface with an acceleration of #0.5 ms^-2#. Determine the acceleration of the trolley after the mass falls off.

2m 42s - 5.
A body initially resting on horizontal frictionless surface is accelerated by a constant force. It passes over a small region where it experiences a force of
friction equal to the accelerating force before returning to the frictionless horizontal surface. On the axis, provided, sketch the velocity – time graph for the motion of the body.

5m 5s - 6.
(a) Two identical spherical steel balls are released from the top of two tall jars containing liquids L1 and L2 respectively.
Figure 3 shows the velocity – time graph of the motion of the balls.
Explain the nature of the curves and state why they are different.
(b) In an experiment to determine the proportionality constant, µ between two wooden surfaces sliding on each other, a block of mass

12m 55s - 7.
Figure 15 shows a tall jar containing two fluids A and B. the viscosity of A is higher than that of B. a solid sphere is released at the top of the
jar and falls through the fluids. On the axis provided, sketch the velocity – time graph for the motion of the spheres through the fluids.

5m 55s - 8.
(a) (i) State one of the Newton’s law of motion.
(ii) A body resting on a horizontal surface is given an initial velocity V so that it slides on the surface for some distance before coming
to a stop. Table 1 shows the distance d moved by the body of various values of V.
Given that #V^2# = 20µd where µ is a constant for the surface, plot an appropriate graph and use it to determine µ.

10m 44s - 9.
A high jumper usually lands on thick soft mattress.
Explain how the mattress helps in reducing the force of impact.

2m 53s - 10.
A resultant force F acts on a body of mass m causing an acceleration #a_1# on the body.
When the same force acts on a body of mass 2m, it causes an acceleration #a_2#. Express #a_2# in terms of #a_1#.

2m 46s - 11.
A trolley is moving at a uniform speed along a track. A piece of plasticine is dropped on the trolley and sticks on it. Explain why the trolley slows down.

2m 22s - 12.
Figure 14 shows the velocity– time graph for a small metal sphere falling through a viscous fluid.
On the axis provided, sketch the graph of momentum against time for the same mass.

2m 41s - 13.
A footballer kicks a ball of mass 0.6 kg initially at rest using a force of 720N. if the foot was in contact with the ball for 0.1 seconds, what was the takeoff speed of the ball?

2m 46s - 14.
(a) State newton’s first law of motion.
(b) A wooden block resting on a horizontal bench is given an initial velocity, u, so that it slides on the bench surface for a distance, n, before
coming to stop. The values of d were measured and recorded for various values of initial velocity.
Figure 10 shows the graph of #u^2# against d.
(i) Determine the slope, s, of the graph.
(ii) Given that #u^2#= 20k

11m 54s - 15.
State Newton’s second law of motion.

1m 23s - 16.
A cart of mass 30kg is pushed along a horizontal path by a horizontal force of 8N and moves with a constant velocity. The force is then increased to 14N.
Determine:
(a) The resistance to the motion of the cart
(b) The acceleration of the cart.

3m 0s - 17.
(a) Figure 12 shows a lorry towing a trailer using a rope.
The lorry exerts a force N on the trailer and the trailer exerts an equal but opposite force M on the lorry. The frictional force between the trailer and the road is F. Explain how the forces N, M and F enable the trailer to move.
(b) Figure 13 shows a frictionless trolley of mass 2kg moving with uniform velocity towards a wall. At the

5m 41s - 18.
A student pulls a block of wood along a horizontal surface by applying a constant force. State the reason why the block moves at a constant velocity.

2m 22s - 19.
Figure 9 shows a trolley on a smooth surface being pulled by a constant force F.
(i) On the axis provided, sketch the velocity –time graph for the motion of the trolley.
(ii) A parachute falling through the air attains terminal velocity after a short time. State the reason why it attains terminal velocity.

3m 9s - 20.
A horizontal force of 12N is applied on a wooden block of mass 2kg placed on a horizontal surface. It causes the block to accelerate at 5
#ms^-2#. Determine the frictional force between the block and the surface.

2m 3s - 21.
Using the definition of impulsive force, show that F=ma.

2m 5s - 22.
(a) A wooden block resting on horizontal bench is given an initial velocity u so that it slides on the bench for a distance X before it stops. Various
values of X are measured for different values of the initial velocity. Figure 9 shows a graph of #u^2# against x.
(i) Determine the slope S of the graph.
(ii) Determine the value of k, given that #u^2# = 20kd where k is a frictional constant for the

7m 42s - 23.
Two boxes E and F of masses 2.0kg and 4.0kg respectively are dragged along a frictionless surface using identical forces. State with a reason which box
moves with a higher velocity.

2m 16s - 24.
Figure 8 shows the graph of velocity against time for a small steel ball falling in a viscous liquid.
(i) Describe the motion of the steel ball as represented by part OA.
(ii) Explain why the velocity between A and B is constant.

5m 53s - 25.
(a) A student kicked a ball vertically upwards with an initial velocity of 8mls. Determine:
i) The time taken to reach maximum height
ii) The maximum height reached by the ball
(b) In a hockey match, a player hit a stationary ball of mass 800g with a force of 500N using a hockey stick. Find the velocity with which the ball leaves if the stick and ball are in contact for 0.02 seconds.

6m 5s - 26.
An object of the mass 150kg moving at 20m/s collides with a stationary object of mass 90kg.They couple after collision
.Determine the :
i).Total momentum before collision
ii) Total momentum after collision
iii) Their common velocity after collision

2m 44s - 27.
a) A boy throws a tennis ball vertically upwards from a truck moving at a constant velocity. Give the reason why the ball lands back exactly the same point where it was projected.
b) Define impulse in terms of momentum.
c) A trailer of mass 30 tonnes travelling at a velocity of 72km/h rams onto a stationary bus of mass10 tonnes.
The impact takes 0.5 seconds before the two vehicles move off

9m 46s - 28.
A ball of mass 0.75kg rests on the surface of a level bench.
i).Draw a sketch showing the forces acting on the ball and give the magnitude of the forces.
ii) If the ball was raised 1.5m above the surface and then released, what would be its Kinetic energy just before hitting the surface?

2m 37s - 29.
A body initially moving at 50 m/s decelerates uniformly at 2 m/s² until it comes to rest. Calculate the distance covered by the body.

2m 27s - 30.
An external force applied to a ball of mass 160 g increases its velocity from 25 cm/s to 275 cm/s in 10 Seconds. Calculate the force applied.

3m 7s - 31.
A tennis ball of mass 100 g is struck by a tennis racket. The velocity of the ball is changed as shown. What is the magnitude of the change in momentum of the ball?

4m 4s - 32.
What happens according to Newton if you let an untied balloon go?

0m 38s - 33.
Describe what happens if you are riding a skateboard and hit something (like a curb) with the front wheels.

1m 4s - 34.
Describe why you hold your gun next to your shoulder while firing a bullet out.

0m 52s - 35.
What is another name for the first law of motion? Why is it given that name?

3m 30s - 36.
What is the net force required to give an automobile of mass 1600 kg an acceleration of 4.5 m/s^2

1m 30s - 37.
Find the net force on each box.

2m 12s - 38.
What is the acceleration of a wagon of mass 20 kg if a horizontal force of 64 N is applied to it? (Ignore friction)

1m 13s - 39.
A girl of mass 50 kg stands inside a lift which is accelerated upwards at a rate of 2 m/#s^2#. Determine the reaction of the lift at the girls’ feet.

2m 21s - 40.
A bullet of mass 0.005 kg is fired from a gun of mass 0.5 kg. If the muzzle velocity of the bullet is 350 m/s, determine the recoil velocity of the gun.

2m 34s - 41.
A minibus of mass 1,500 kg travelling at a constant velocity of 72 km/h collides head-on with a stationary car of
mass 900 kg. The impact takes 2 seconds before the two move together at a constant velocity for 20 seconds.
Calculate
a).The common velocity
b).The distance moved after the impact
c).The impulsive force
d).The change in kinetic energy

9m 29s - 42.
A box of mass 50 kg is dragged on a horizontal floor by means of a rope tied to its front. If the coefficient of kinetic friction between the floor and the box is 0.30, what is the force required to move the box at uniform speed?

1m 55s - 43.
A block of metal with a mass of 20 kg requires a horizontal force of 50 N to pull it with uniform velocity along a
horizontal surface. Calculate the coefficient of friction between the surface and the block. (take g = 10 m/s)

0m 0s - 44.
State six laws of friction

3m 25s