Question

Consider a perfectly inelastic head-on collision between a small car and a large truck traveling at the same speed. Which vehicle has a greater change in kinetic energy as a result of the collision?

Since the vehicles stick together after the collision and take the direction of the large truck (greater momentum), I guessed that the small car would have a greater change in kinetic energy.

I can easily use formulas to find answers, but I always have trouble with conceptual questions like this.

Answer 1

Hmmmm. What is a perfectly inelastic collision as compared to an inelastic collision?

Momentum is conserved.

Mv-mv= initial momentum
after the collision...
Mv-mv=(M+m)v'

now which is greater?
v-v', or -v-v' Obviously, the smaller mass is greater (-v-v').