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The tension in the cable that holds an elevator is equal to the elevator’s weight. What can be inferred about the motion of the elevator?

1. It is moving upward or downward with constant speed
2. It is moving upward or downward with constant acceleration
3. It is moving upward or downward with changing acceleration
4. It may be either moving with constant acceleration or with changing acceleration

Correct answer: It is moving upward or downward with constant speed

Solution

If tension equals weight, net force is zero, so acceleration is zero. Zero acceleration means the elevator moves with constant velocity (constant speed) up or down, or stays at rest.

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