The Total solution for NCERT class 6-12
On a long horizontally moving belt figure, a child runs to and fro with aspeed 9 km h–1 (with respect to the belt) between hisfather and mother located 50 m aparton the moving belt. The belt moves witha speed of 4 km h–1. For an observer on astationary platform outside, what isthe(a) speed of the child running in thedirection of motion of the belt ?.(b) speed of the child running oppositeto the direction of motion of the belt?(c) time taken by the child in (a) and(b)?Which of the answers alter if motion isviewed by one of the parents?
Speed of child = 9 kmh-1
Speed of belt = 4 km h-1(a) When the boy runs in the direction of motion of the belt, then his speed asobserved by the stationary observer = (9 + 4) km h-1 = 13 km h-1.
(b) When the boy runsopposite to the direction of motion of the belt, then speed of child asobserved by the stationary observer = (9 – 4) km h-1 = 5 km h-1
(c) Distancebetween the two parents = 50 m = 0.05 km
Speed of the boy asobserved by both the parents is 9 km h-1
Time taken by the boyto move towards one of the parents =0.05 km/9k h-1=0.0056 h =20 S