When it crashes into a bridge support that does not move, a car goes from 120km/

Question

When it crashes into a bridge support that does not move, a car goes from 120km/h to 0 in 1.23 m.

A) What is the impulse delivered to the 70-kg driver by the seat belt, assuming the belt makes the driver's motion identical to the car's motion? Assume that the initial direction of motion of the car is the positive direction

B) What is the average force exerted by the belt on the driver?

C) If the driver were not wearing the seat belt and flew forward until he hit the steering wheel, which stopped him in 0.0145 s, what would be the average force exerted by the steering wheel on him?

Explanation / Answer

Note that

J = m(vf - vi)

Here,

vf= 0 m/s
vi = 120 kph = 33.333 m/s

Thus,

J = -2333 N*s   [ANSWER]

****************

We first get the acceleration,

a = (vf^2 - vi^2) / 2d

Thus,

a = 451.66 m/s^2

Thus,

t = (vf - vi)/a

t = 0.0738 s

Thus,

F = J/t

F = -31600 N   [ANSWER]

*************

This time, t = 0.0145 s,

F = J/t

F = -161000 N [ANSWER]

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