Initially car `A` is `10.5 m` ahead of car `B`. Both start moving at time `t = 0` in the same direction along a straight line. The velocity-time graph of two cars is shown in figure. The time when the car `B` will catch the car `A`, will be.

Options

A. `t-21` sec
B. `t=2sqrt(5)` sec
C. `20` sec
D. None of these

Answer

A

Explanation

`S_(B)=S_(A)+10.5`
`t^(2)/2=10t+10.5`
`t^(2)=20t+21`
`t^(2)-20t-21=0`
`t=21` sec