# Car collision

1. Nov 20, 2005

### Erik_at_DTU

Hey,

I've been looking on this problem:

"You have two cars with equal mass and speed (50km/h), which crash head on. One driver is wearing a seat belt (situation 1), the other not (situation 2). Calculate the force and impulse on each of the drivers during the collision. You can assume that the forces on the cars is constant (the deacceleration is constant). Make necessary assumptions."

My evaluation:
Both situations can be analysed as a car hitting a wall, because the cars have the same mass and speed. I assume that the car has a deformation length s=0.5 meter.
Situation 1:
The seat belt is a non stretching version, and calculate the acceleration a=192.9m/s^2. And the time it takes to stop t=0.072 s. Is this correct?

Situation 2:
This is a much more difficult situation to analyse, because the driver will be thrown out of his seat and hit the front window (which I assume is aligned vertical) with the same speed the car had before the crash (50km/h). But the car will have a different speed so relative to the car the person will have a speed=(the person's speed relative to the road) - (the cars speed relative to the road). So here I'm stuck, so I cry into the physics jungle for help :tongue2:

Anyone who have the opportunity to take a look at it?

2. Nov 21, 2005

### mezarashi

Assume the change in momentum of both cars is the same, then the change in momentum of both drivers is also the same.

An impulse is needed to change the momentum. The impulses therefore must be the same. The impulse is a product of force and time. The seatbelt case will be more restrictive thus take less time. He will feel more force. The guy without the seatbelt will feel less force, but unfortunately he will be flying out the windshield into god knows what.

It'd be easier to assume an impact time, but using a deformation length is okay too ^_^