CAIE IGCSE Physics Conservation of Momentum

Practise conserving signed momentum in one-dimensional collisions and separations, then solve for an unknown mass or velocity with a stated direction.

Exam points

assign opposite velocity signs and calculate total momentum before the interaction
equate total momentum before and after, then solve for an unknown mass or velocity
state the final direction from the sign of the calculated velocity or momentum

[Maximum number: 4]

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

(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

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1.6.3—Apply the principle of the question 1