AP Physics 1 Question 95: Answer and Explanation
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A 0.5 kg cart begins at rest at the top of an incline, 0.06 m vertically above its end position. It is released and allowed to travel down the smooth incline, where it compresses a spring. Between the positions labeled "Begin" and "End" in the figure, the work done on the cart by the earth is 0.30 J; the work done on the cart by the spring is –0.20 J. What is the cart’s kinetic energy at the position labeled "End"?
- A. 0.80 J
- B. 0.10 J
- C. 0.50 J
- D. 0.40 J
Correct Answer: B
B-Consider the cart alone, which as a single object has no internal energy or potential energy. Thus, any work done on the cart will change the cart's kinetic energy. The cart began with no kinetic energy at all. Earth increased the cart's kinetic energy by 0.30 J, as stated in the problem; the spring decreased the cart's kinetic energy by 0.20 J. A gain of 0.30 J and a loss of 0.20 J leaves 0.10 J of kinetic energy.