A car moves from `X` to `Y` with a uniform speed `v_u` and returns to `Y` with a uniform speed `v_d`. The average speed for this round trip is :

Options

A. `(v_(u)+v_(d))/(2)`
B. `(2v_(d)v_(u))/(v_(d)+v_(u))`
C. `sqrt(v_(u)v_(d))`
D. `(v_(d)v_(u))/(v_(d)+v_(u))`

Answer

B

Explanation

Average speed `=("Total distance")/("Total time")`
`=(2d)/((d)/(v_(u))+(d)/(v_(d)))=(2v_(d)v_(u))/(v_(d)+v_(u))`