Two 5-N boxes are attached to opposite ends of a spring scale and suspended from pulleys as shown.
-Suppose that the system were placed in an elevator that accelerates downward at 2 m/s². What would the scale read?

Question

Two 5-N boxes are attached to opposite ends of a spring scale and suspended from pulleys as shown.

-Suppose that the system were placed in an elevator that accelerates downward at 2 m/s². What would the scale read?

Quizplus · Accepted Answer

The force of gravity on each box is 5 N, so the total weight of the system is 10 N. When the elevator accelerates downward at 2 m/s^2, the net force on the system is (10 N) - [(2 m/s^2)(10 N)] = 6 N (downward). Therefore, the scale would read 6 N - the weight of one of the boxes (5 N) = 1 N. However, since there are two boxes, we need to multiply by 2 to get the total reading of the scale: 2 N + 2 N = 4 N. Therefore, the correct answer is D.

Two 5-N Boxes Are Attached to Opposite Ends of a Spring