Answer –
According to the question, speed of child is 9 km h-1 speed of the belt is 4 km h-1
(a) When the boy runs in the belt’s direction of motion, his speed as measured by a stationary observer equals :
= (9 + 4) km h-1
= 13 km h-1.
(b) When the boy runs in the opposite direction of the belt’s motion, the child’s speed as measured by a stationary observer
= (9 – 4) km h-1
= 5 km h-1
(c) And the distance between the two parents is 50 m, or 0.05 km
We know that the speed of the boy for both the parents is 9 km h-1
Therefore, the time taken by the boy to move in direction of one of the parents is
=0.05 km/9k h-1
=0.0056 h
=20 seconds