- #1

xxphysics

- 38

- 3

## Homework Statement

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

## Homework Equations

F = m*a

J = delta p

p = m*v

## The Attempt at a Solution

So I got part A, -1650 N*s, by just converting 85 km/h to 23.61 m/s and multiplying that by the mass (70 kg). Then for part B I found what I thought was the acceleration by dividing the 23.61 m/s velocity by 1.23 m (73.8 s). I got 0.319992 m/s^2 and multiplied that by the 70 kg mass to get the force. This gave me an answer of -22 N, which was wrong. I then checked to see if I interpreted the "1.23 m" wrong, checking to see if I should've used 83 s instead of 73.8 s, and got - 20 N but this was still wrong.

What am I doing wrong?