5.9.3 Collisions

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Example: Calculations involving momentum with a collision Two cars crash head-on into each other and both come to rest. The momentum after the crash is 0kg m/s. The diagram shows the velocities and masses of the two cars before the collision. Calculate the velocity of car A before the collision, $vA$ . Momentum is conserved. [3 marks]

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Calculation If the momentum after the collision is 0kg m/s, then the momentum before the collision must also be 0kg m/s.

Therefore the momentum of the two vehicles must add up to zero. This means the momentum of each vehicle must be equal:

Momentum of Car A = Momentum of Car B

Using the momentum equation, $p =mv$ :

mA×vA=mB×vB

Substitute in the values:

1000kg×vA=1500kg×9m/s

Rearrange to find the velocity of Car A:

vA= \frac{1500×9 }{1000}

vA =:success[13.5m/s]

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