A student walks in a straight line along the east–west direction. He first walks 50m east from his home to a bookshop, stops briefly, and then walks 20m west towards his home.
(i) Draw a neat, labelled position–time graph (taking east as positive) for the entire motion.
(ii) Using the graph, or otherwise, find the total distance travelled and the magnitude of the net displacement.
(iii) Explain why the magnitude of displacement is smaller than the distance in this situation.