Question

During a car accident, a 125 kg driver is moving at 31 m/s and in 1.5 seconds is brought to rest by an inflating air bag. What is the magnitude of the change in momentum of the driver?

A. 4.0 kg • m/s
B. 21 kg • m/s
C. 47 kg • m/s
D. 3900 kg • m/s

Answer 1

D. 3900 kg • m/s

Step-by-step explanation:

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Answer 2

The momentum of a moving object is given by:

`p=mv`
where
m is the mass
v the velocity of the object

Before the car accident, the driver (of mass m=125 kg) was moving at speed v=31 m/s, so his initial momentum was

`p_i = mv=(125 kg)(31 m/s)=3875 kg m/s \sim 3900 kgm/s`

However, after the collision the driver is brought to rest: it means his final velocity is zero, and so also his final momentum is zero:
`p_f=0`. Therefore, the change in momentum of the driver is equal to his initial momentum:

`\Delta p = 3900 kg m/s`
and the correct answer is D.