SAT Subject Physics Practice Question 586: Answer and Explanation
12. A 1,000 kg car rolls without friction down a hill that is 20 m long and inclined at 15°C from the horizontal. What is the velocity of the car at the bottom of the hill?
A. 2 m/s
B. 5 m/s
C. 10 m/s
D. 20 m/s
E. 30 m/s
Correct Answer: C
The correct answer is (C). The car rolls down a 20 m long incline that is raised at 15° from the horizontal. Using trigonometry (sin 15°)(20 m) we find the car "falls" 5.125 m. Using the PE = KE relationship, we have mgh = .5mv2. The masses factor out, leaving gh = .5v2, leading to v = . The answer is 10 m/s.