An automobile travelling with a speed `60 km//h` , can brake to stop within a distance of `20 m` . If the car is going twice as fast i. e. , `120 km//h`, the stopping distance will be

Options

A. 20 m
B. 40 m
C. 60 m
D. 80 m

Answer

D

Explanation

Let a be the retardation for both the vehicles.
For automobile , `v^(2) =u^(2) -2aS`
`:. U_(1)^(2) - 2aS_(1) = 0 " or " u_(1)^(2)=2aS_(1)`
Similarly for car , `u_(2)^(2) = 2aS_2`
`:.((u_2)/u_1)^2=S_2/S_1" or " ((120)/60)^2 =S_2/20`
or `S_(2) = 80 m `