Truck and car collision problem

[dominus96]

Homework Statement

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?

Homework Equations

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

The Attempt at a Solution

I don't know what to do...

 

[Doc Al]

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.)

 

[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?

 

[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?

 

[Doc Al]

Their final speed would be 0, right?

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.)

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?

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