CAIE IGCSE Physics Momentum Question Bank

Practise momentum, impulse, force-time and collision calculations, retaining velocity direction and applying conservation of total momentum to interacting objects.

Exam points

calculate vector momentum with p = mv and use a sign convention for opposite directions
relate impulse FΔt to change in momentum and rearrange for average force or stopping time
equate total momentum before and after a collision or separation to solve an unknown mass or velocity

Covered syllabus points

1.6.1—Momentum as mass × velocity 1.6.2—Impulse as force × time for which 1.6.3—Apply the principle of the 1.6.4—Resultant force as change in momentum

[Maximum number: 7]

(a)

Define momentum.

[ 1 ]

(b)

Fig. 3.1 shows two toy trains, A and B , on a track.

Fig. 3.1

The mass of train A is 0.45 kg and the mass of train B is 0.21 kg. The trains do not have motors.

Train A travels towards train B and they collide.

Immediately before the collision:
- the velocity of train A is $0.34 \mathrm{~m} / \mathrm{s}$ to the right
- the velocity of train B is $0.12 \mathrm{~m} / \mathrm{s}$ to the left.

The trains stick together when they collide.
Calculate the velocity of the trains immediately after the collision.
velocity =
direction

[ 4 ]

(velocity =) $0.19 \mathrm{~m} / \mathrm{s}$ AND (direction) to the right

A4

( momentum before collision $)=\{0.45 \times 0.34\}-\{0.21 \times 0.12\}$ OR 0.1278

C1

(momentum after collision) $=0.66 \times v$

C1

momentum before collision = momentum after collision
$\text { OR }\{0.45 \times 0.34\}-\{0.21 \times 0.12\}=0.66 \times v \text { OR } 0.153-0.0252=0.66 \times v$

C1

(c)

A different train is travelling with a momentum of $0.26 \mathrm{~kg} \mathrm{~m} / \mathrm{s}$ .

The train slows down and stops after 2.1 s .
Calculate the average force acting on the train during this time.

average force =

[ 2 ]

$(-) 0.12 \mathrm{~N}$

A2

$F \Delta t=\Delta\{m v\} \mathbf{O R}(F=) \Delta p \div(\Delta) t \mathbf{O R}(F=) \Delta\{m v\} \div(\Delta) t \mathbf{O R}(F=) 0.26 \div 2.1$

C1

[Maximum number: 1]

A ball is at rest on the ground. A boy kicks the ball. The boy's boot is in contact with the ball for a time of 0.040 s .

The average force on the ball is 200 N . The ball leaves the boy's boot with a speed of $20 \mathrm{~m} / \mathrm{s}$ .
Which row gives the impulse of the boot on the ball and the average acceleration of the ball during the time of 0.040 s ?

impulse on ball
Ns

average acceleration of ball
$\mathrm{m} / \mathrm{s}^{2}$

0.8

500

5000

0.8

5000

500

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Covered syllabus points

1.6 Momentum question 1

Question (a)

Question (b)

Question (c)

1.6 Momentum question 2