Question

An elevator is run by the cables at constant speed. The total work done by the elevator is:

• A. Negative
• B. Positive
• C. Zero
• D. Positive or negative depending on the direction of motion

Answer 1

Answer: (B)

Work done is defined as $W=Fd\cos \theta$

where, $F$ is the force applied, $d$ is the displacement and $\theta$ is the angle between force applied and displacement.

Since, the elevator is moving at a constant speed, the work done is only due to the force of gravity and the tension force exerted on the elevator by the cable which pulls it up. Since, the force of tension and displacement are in the same direction, the angle $\theta =0$ and hence the work done is Positive. Hence, option (B) is correct.