SAT Subject Physics Practice Question 179: Answer and Explanation

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Question: 179


Two cannons shoot cannonballs simultaneously. The cannon embedded in the ground shoots a cannonball whose mass is half that of the cannonball shot by the elevated cannon. Also, the initial speed of the cannonball projected from ground level is half the initial speed of the cannonball shot horizontally from the elevated position. Air resistance is negligible and can be ignored. Each cannonball is in motion for more than 2 seconds before striking the level ground.

For the cannonball of mass m, which of the following quantities decreases as the cannonball falls to the ground?

A. Kinetic energy
B. Potential energy
C. Momentum
D. Speed
E. Mass

Correct Answer: B


As the cannonball falls, it accelerates downward and its speed increases; this eliminates A, C, and D. The mass of the cannonball does not change, eliminating E. The answer is B. As the cannonball falls, its height decreases, so its gravitational potential energy decreases.

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