Between two stations a train starting from rest first accelerates uniformly, then moves with constant velocity and finally retarts uniformly to come to rest. If the ratio of the time taken be `1 : 8 : 1` and the maximum speed attained be `60 km//h`, then what is the average speed over the whole journey ?

Options

A. ` 48 km h^(-1)`
B. `52 km h^(-1)`
C. `45 kmh^(-1)`
D. `56 km h^(-1)`

Answer

C

Explanation

`S_(1)=(1)/(2) at^(2)=(1)/(2)(at) t(60t)/(2) =30t`
`S_(2)=60 xx8t =480t, S3=S_(1)=30t`
.
`v_(av)=(S_(1)+S_(2)+S_(3))/(t+8t+t) =54 km h^(-1)`.