Q 11-02-011NEETJEE MainEAMCET 2010 (Engineering)Top questionEasy
An athlete completes one round of a circular track of radius $R$ in $40$ s. What will be his displacement at the end of $2$ min $20$ s?
Answer: (B) $2R$
Time taken $= 2$ min $20$ s $= 140$ s.
Number of rounds $= \dfrac{140}{40} = 3.5$.
After 3 complete rounds the athlete is back at the start. The extra half round takes him to the diametrically opposite point of the track.
Displacement = the straight-line distance between the start and the end points = the diameter:
$$\text{Displacement} = 2R$$
(The distance travelled is $3.5 \times 2\pi R = 7\pi R$, which is a trap option.)
Solution by Sreeraj P, M.Sc Physics