# Homework Help: Truck and car collision problem

1. Nov 13, 2007

### dominus96

1. The problem statement, all variables and given/known data

Suppose that each vehicle is initially moving at 9.60 m/s and that they undergo a perfectly inelastic head-on collision. Each driver has mass 80.0 kg. Including the masses of the drivers, the total masses of the vehicles are 800 kg for the car and 4000 kg for the truck. If the collision time is 0.120 s, what force does the seat belt exert on each driver:

a) Force on truck driver?

b) Force on the car driver?

2. Relevant equations

P=mv, F=ma, maybe V=V_0+at

3. The attempt at a solution

I don't know what to do...

2. Nov 13, 2007

### Staff: Mentor

This is an impulse problem. Find the change in momentum of each driver. Hint: What's their final speed after the collision? (Don't forget that momentum is a vector--direction counts.)

3. Nov 13, 2007

### dominus96

Their final speed would be 0, right?

But to find force, I need to do mass x acceleration, but I don't know how to find the acceleration. Do I use impulse for that?

4. Nov 13, 2007

### dominus96

Ok I found the force on the truck driver which was 2133.33 N because the truck's final velocity was 6.4 m/s, which was a 3.2 change in velocity, so the acceleration was 26.6666 and I used F=ma to get 2133.33 N. But how do I find it for the car driver?

5. Nov 14, 2007

### Staff: Mentor

No. Use conservation of momentum to figure out the final speed. (Both truck and car will have the same final velocity, since the collision is completely inelastic.)

Use impulse, not mass x acceleration. There's no need to calculate the acceleration. Look up the impulse-momentum theorem.