A car moves a distance of 200 m. It covers first half of the distance at speed 60 `kmh^(-1)` and the second half at speed v. If the average speed is 40 `kmh^(-1)`, the value of v is

Options

A. 30 `kmh^(-1)`
B. 13 `kmh^(-1)`
C. 60 `kmh^(-1)`
D. 40 `kmh^(-1)`

Answer

A

Explanation

Average velocity `= (2v_(1)v_(2))/(v_(1) + v_(2))`
Given `v_(av) = 40 kmh^(-1)`
`v_(1) = 60 kmh^(-1)`
and `v_(2) = ?`
`40 = (2 xx 60 xx v_(2))/(60 + v_(2))`
`80 v_(2) = 2400`
`v_(2) = 30 kmh^(-2)`