A long belt is moving horizontally with a speed of `5 km h^(-1)`. A child runs on this belt to and fro with a speed of `9 km//h` (w.r.t. bett) between his father and mother located `50 m` apart on the belt. For an observer on a stationalry plateform outsied, what is the
(a) speed of the chils runningin the derection of motion of the belt, (b) speed of thechaild runing opposite to thedirection of the belt, and (c ) time taken by the child in cases (a) and (b) ? Which of theanswers change, if motion is viewed by one of the parents ?gt

Explanation

Let us consider left to right be the positive direction of x-axis.
(a) Here, velcity of belt, `v_(B) = +5 km h^(-1)`
Speed of child w.r.t. belt, `v_(C ) =+ 9 km h^(-1)`
`=5//2 ms^(-1)` ltbr Speed of child w.r.t. stationary observer,
`v_(C)' =v_(B) 9+ 5 =14 km h^(-1)`
(c ) Distance between parents, `s=50 m`.
Since parents and child are located on the same belt, the speed of child as observed by stationary observer ineither direction (eitgher from mother tofather or from father to mother ) will be `9 kmh^(-1). Time taken by child in case (a) and (b) is,
`t=50//(5//2) =20 s`
If the motion is observed by one of the parents, answer to case (a) or case (b) will ger alterd. It is so because speed of child w. r. t. either of mother or father is `9 km// h.
But answer (c ) remains unalterd due to the fact that parents and child are on the same belt and as such all are equally afferted by the motion of belt.