Exercise 4.1
In the example of an athlete running back and forth on a straight track (Fig. ), when will the displacement of the athlete be zero? What will be the total distance travelled in that case?
Not cross-checked
NCERT prints no numerical answer for this exercise, so this working has not been cross-checked against the book.
The displacement is zero whenever the athlete is back at her starting point O, because her position at the final instant is then the same as her position at the first instant.
In Fig. $\displaystyle 4.4$ this happens if she runs from O out to A and then returns all the way to O, instead of stopping at B.
The total distance in that case is \(\displaystyle \text{OA} + \text{AO} = 100\ \text{m} + 100\ \text{m} = 200\ \text{m} \).
So zero displacement does not mean zero distance — distance keeps adding up along the whole path travelled, while displacement only compares the two end positions.
