question_answer

The displacement-time graph of a lift climbing up from the ground floor to the top of a building is given in the figure alongside. Using this graph, answer the following: (a) What are the states of motion at A, B and C? (b) Plot the velocity-time graph of the lift.

Answer:

At A: The lift is on the ground floor and is stationary, i.e., it is at rest. At B: The lift is under accelerated motion from A to B. At B, its velocity is the maximum: the slope of the curve at point B is the highest. At C: The slope of displacement-time graph is zero. So, the lift is at a halt at some higher floor. The velocity of the lift at any point of time is given by the slope of its displacement-time graph at that point. The graph shows that slope of the curve increases gradually from A to B, reaches a maximum at B(t = 5 s) and then decreases to become zero at C (t = 7 s).