Question

Is displacement-time graph different from distance time graph? How? Explain with an example.

Answer 1

A displacement time graph simply shows where an object is at a given time. Consider a train on tracks - let's let 'X' be the distance from the end of the tracks. As the train leaves the station, X increases. The rate of increase depends solely on how fast it is going (steeper=faster). After an hour, the train stops (so the graph goes flat) and then goes back to where it started. At the point in the graph, the displacement goes DOWN - as the distance from the end of the tracks is now decreasing (since the train is returning home). When the train reaches home, the displacement is zero.

A distance-time graph, in essence, doesn't care in what direction the train is travelling. It does not give a unique answer to "where is the train at time X" - only how far it has driven. Imagine the train simply driving forward 1m, then backwards 1m, for 10 minutes. Ignoring acceleration time, this would be indistinguishable from the train simply going straight on for the same length of time. A distance time graph can never go back to zero - it is always increasing.