PHYSICS · Subjective · A Level · Physics · Mechanics and materials · Mechanics and materials
Problem
A particle moves along a straight vertical line. The following description summarises its motion:
• From t=0s to t=2s the particle moves upward while gradually coming to rest.
• From t=2s to t=4s it reverses and moves downward, gaining speed.
• From t=4s to t=5s it continues downward but loses speed and comes momentarily to rest at t=5s.
Taking the upward direction as positive, answer the following:
(i) For each of the three time intervals, state the sign (positive, negative or zero) of (a) velocity and (b) acceleration.
(ii) Give a clear verbal justification for the sign of acceleration in every interval without using numerical calculations.
(iii) Would any of your answers change if the downward direction were taken as positive instead? Explain briefly.