When it crashes into a bridge support that does not move, a car goes from 85km/h

Question

When it crashes into a bridge support that does not move, a car goes from 85km/h to 0 in 1.23 m.

Part 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.

Express your answer to two significant figures and include the appropriate units.

Part B

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

Part 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?

Express your answer to two significant figures and include the appropriate units.

Explanation / Answer

Part A)

The initial speed of 85 km/hr converts to 23.61 m/s

The impulse is the change in momentum

Impulse = mv

Impulse = (70)(23.61) = 1653 Ns

Part B)

We need the time to stop

Apply d = (.5)(vf + vo)(t)

1.23 = (.5)(0 + 23.61)(t)

t = .104 sec

Then Impulse = Ft

1653 = F(.104)

F = 15866 N which is (1.59 X 104 N)

Part C)

1653 = F(.0145)

F = 114000 N which is (1.14 X 105 N)

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