Net Force of Car: Solving for 70kg Driver Deceleration

[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 .

Homework Equations

I am having trouble setting this problem up can someone help

The Attempt at a Solution

 

[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.

 

[pats6]

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

 

[mgb_phys]

No there are three equations for motion you need to learn
See here https://www.physicsforums.com/showthread.php?t=110015 post #2

You want the one which only has initial velocity, final velocity, distance, accelration

 

[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