Question

You are driving your small, fuel-efficient car when you have a head-on collision with a big, fuel-efficient truck that is three times as massive as your car. Head-on means, for example that if you are traveling in the positive x direction, the truck is traveling in the negative x direction. Right before the collision, you were traveling at a speed of 3.0 m/s and right after the collision, both vehicles are at rest. Due to the conservation of the momentum, you can find the speed of the truck before the collision. What was the kinetic energy of the truck Ktruck before the collision when the kinetic energy of the car was Kcar

Answer 1

Explanation:

Momentum before = momentum after

mv + MV = 0

(m) (3.0 m/s) + (3m) (V) = 0

V = -1.0 m/s

The truck was moving at 1.0 m/s before the collision.

The kinetic energy of the car was:

KE = 1/2 m v²

Kcar = 1/2 m (3.0)²

Kcar = 9/2 m

Ktruck = 1/2 M V²

Ktruck = 1/2 (3m) (1.0)²

Ktruck = 3/2 m

Ktruck = 1/3 Kcar

So the truck had 1/3 the kinetic energy of the car.