Question

A lift is descending with uniform speed from 4th floor and is just about to reach 2nd floor . Taking origin at ground floor and upward direction as positive for all quantities , which one of the following is correct?

• A. Displacement > 0 , velocity > 0
• B. Displacement < 0 , velocity > 0
• C. Displacement > 0 , velocity < 0
• D. Displacement < 0 , velocity < 0

Answer 1

The correct option is D Displacement < 0 , velocity < 0

Displacement < 0, Velocity < 0

Here the upward direction positive. As. the lift is coming in downward direction, the displacement will be negative. We have to see whether the motion is accelerating or retarding.

We know that due to downward motion displacement will be negative. When the lift reaches 2nd floor and is about to stop velocity is decreasing with time, hence motion is retarding in nature.

Thus, x < 0; a > 0.

As displacement is in negative direction, velocity will also be negative, i.e. v < 0.
The motion of lift will be shown like this.