You are a traffic accident investigator. You have arrived at the scene of an accident. Two trucks of equal mass (3,000 kg each) were involved in a rear-end accident at a stop sign. Here is what you know: Truck 1 started from rest at the top of a 22-meter hill and coasted toward the intersection.

Truck 2 was on a flat stretch of road at the bottom of the hill directly in front of Truck 1.
At the bottom of the hill, Truck 1 was going 20 m/s; Truck 2 was going 35 m/s.

There were no skid marks left by Truck 2. The collision occurred at the stop sign where Truck 2 had stopped.

After the collision, both trucks moved together in the same direction at 10 m/s before slowly rolling to a stop.

You must now push Truck 2, using 1,000 N of force, 8 meters off to the side of the road so no one else gets hurt.

1. What was the potential energy of Truck 1 at the top of the hill? (3 points)

3000 x 9.81 x 22 = 647,460 J

2. What was the kinetic energy of each truck before they began braking? (4 points)

Truck 1: 600,000 J
Truck 2: 1,837,500 J

3. A. How much energy did Truck 1 lose from the top to the bottom of the hill? (3 points)

47,460

B. Where do you suppose that energy went? (2 points)

I suppose that the energy converts into heat and sound that is felt during the crash.

4. How much work was done to bring Truck 2 to a stop? (4 points)
5. If Truck 2 came to a stop in 15 seconds, how much power (in watts) did it take to stop Truck 2 at the stop sign by applying force to the brakes? (3 points)

6. What is the final combined momentum of the trucks right after the accident? (6 points)

7. Assuming that there are no other nonconservative forces involved, what impulse was given to each truck during the collision? (6 points)

A. Truck 1: (3 points)

B. Truck 2: (3 points)

8. How much energy did Truck 1 lose in the collision? (3 points)

9. How much energy did Truck 2 gain in the collision? (3 points)

10. Which of the two laws covered in this unit - Law of Conservation of Momentum or Law of Conservation of Energy - is obeyed in this problem? Explain your reasoning. (5 points)

11. How much work did it take to move Truck 2 off to the side of the road? (3 points)

12. If it took you 40 seconds to move Truck 2 off the road, how much power did you expend? (3 points)

13. Which simple machine does a truck have that helped you move Truck 2? Explain. (2 points)