During the first `18 min` of a `60 min` trip, a car has an average speed of `11 ms^-1.` What should be the average speed for remaining `42 min` so that car is having an average speed of `21 ms^-1` for the entire trip?

Options

A. `25.3 ms^-1`
B. `29.2 ms^-1`
C. `31 ms^-1`
D. `35.6 ms^-1`

Answer

A

Explanation

`v_(av)=d/t=(d_1+d_2)/(t_1+t_2)`
`21=((18)(11)+(42)(v))/60`
`rArr v=25.3m//s`