A motor vehicle travelled the first third of a distance s at a speed of `v_1`=10 kmph, the second third at a speed of `v_2`=20 kmph and the last third at a speed of `v_3`=60 kmph. Determine the mean speed of the vehicle over the entire distance s.

Explanation

`v_(1)`=10kmph,`v_(2)`=20,`v_(3)`=60,v=?
`(3)/(v)=(1)/(v_(1))+(1)/(v_(2))+(1)/(v_(3)),(3)/(v)=(1)/(10)+(1)/(20)+(1)/(20)+(1)/(60)=0.1+0.05+0.016`
`therebore V=(3)/(0.166)`=18 kmph