A motorcyclist drives from `A` to `B` with a uniform speed of `30 km h^(-1)` and returns back with a speed of `20 kmh^(-1)`. Find its average speed.

Options

A. `25 kmh^(-1)`
B. `24 kmh^(-1)`
C. `50 kmh^(-1)`
D. `10 kmh^(-1)`

Answer

B

Explanation

`upsilon_(AB)`= speed of car from A to B

`upsilon_(AB)=30 kmh^(-1)`
`upsilon_(BA)=` speed of car from B to A
`upsilon_(BA)=20 kmh^(-1)`
`upsilon_(av)=(2upsilon_(AB)upsilon_(BA))/(upsilon_(AB)+upsilon_(BA))=24 kmh^(-1)`