Question

when is the elevator on the third floor again?
o a. s to t only
o b. q to r and s to t
o c. q to r only
o d. the lift does not return to the third floor.

Explanation:

Step1: Analyze the velocity - time graph

In a velocity - time graph, when the velocity is zero, the elevator is at rest (not moving). If the elevator was at the third floor (a particular position) and then moves (velocity non - zero) and comes back to rest (velocity = 0), it may be at the same position (third floor) again.

Step2: Check the intervals

• In the interval \(Q - R\), the velocity is zero. This means the elevator is at rest. If it was at the third floor before moving (before \(Q\)) and comes to rest at \(Q - R\), it could be at the third floor.
• In the interval \(S - T\), the velocity is zero. But there is no indication that the elevator was at the third floor before \(S\) (because the negative velocity before \(S\) implies it was moving in the opposite direction from the initial upward motion).

Answer:

C. Q to R only