SAT Subject Physics Practice Question 217: Answer and Explanation

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Question: 217


The four forces act on the block as it moves the distance L. What is the total work performed on the block by these forces?

A. (F + f)L
B. (F − f)L
C. (N − w)L
D. (N + w)L
E. (F − N + f − w)L

Correct Answer: B


Because the forces N and w are vertical while the displacement of the block is horizontal, the work done by each of these forces is zero, so they contribute nothing to the total work performed. This eliminates C, D, and E. Since the force f is opposite to the direction of the displacement, the work it does is negative; in fact, it’s –fL. The work done by the force F is FL, so the total work performed on the block is –fL + FL = (Ff)L.

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