# Physics

Instructions: Read the following paragraph carefully. Then use what you know about momentum, work, and energy to answer the following questions. Be sure to show your work.
You are a traffic accident investigator. You have arrived at the scene of an accident. Two cars of equal mass (1,000 kg each) were involved in a rear-end accident at a stop sign. Here is what you know:

Car 1 approached the intersection from the top of a 25-meter hill.
Car 2 was on a flat stretch of road directly in front of Car 1.
At the bottom of the hill, Car 1 was going 20 m/s; Car 2 was going 30 m/s before it stopped at the stop sign.
There were no skid marks left by Car 2. The collision occurred at the stop sign, where Car 2 had stopped.
After the collision, both cars were moving together in the same direction at 10 m/s before slowly rolling to a stop.
You must now push Car 2, using 800 N of force, 10 meters off to the side of the road so no one else gets hurt.
1. What was the potential energy of Car 1 at the top of the hill?

2. What was the kinetic energy of each car before braking?

3. A. How much energy did Car 1 lose from the top to the bottom of the hill?

B. Where do you suppose that energy went?

4. How much work was done to bring Car 2 to a stop?

5. If Car 2 came to a stop in 15 seconds, how much power (in watts) did it take to stop Car 2 at the stop sign by applying force to the brakes?

6. What is the final combined momentum of the cars right after the accident?

7. Assuming that there are no other nonconservative forces involved, what impulse was given to each car during the collision?
A. Car 1

B. Car 2

8. How much energy did Car 1 lose in the collision?

9. How much energy did Car 2 gain in the collision?

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.

11. How much work did it take to move Car 2 off to the side of the road?

12. If it took you 40 seconds to move Car 2 off the road, how much power did you expend?

13. Which simple machine does a car have that helped you move Car 2? Explain.

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