# Net Force of car

1. Feb 18, 2009

### pats6

1. The problem statement,

A driver wearing a seatbelt decelerates at roughly the same rate as the car itself. Since modern cars have a "crumple zone" built into the front of the car, the car will decelerate over a distance of roughly 1.0 . Find the net force acting on a 70-kg driver who is decelerated from 21m/s to rest in a distance of 1.0m .

2. Relevant equations

I am having trouble setting this problem up can someone help

3. The attempt at a solution

2. Feb 18, 2009

### mgb_phys

First you need the acceleration.
They decelerate from 21m/s to 0 in 1.0m. Which motion equation only has speed, acceleration and distance ?

Then you need the equation the relates force, mass and acceleration.

3. Feb 18, 2009

### pats6

Is d = vt + (1/2)at^2 the right formula if so we do not have time

4. Feb 18, 2009

### mgb_phys

5. Feb 18, 2009

### pats6

ok so i would use v^2= Vo^2+2aDx
That woud give me acceleration and then I would use F=ma and use the mass of driver and the acceleration calculated to find the net force