Correct Answer - D
Let the car accelerate at rate `alpha` for time `t_1` then maximum velocity attained, `v = 0 + alpha t_1 = alpha t_1`
Now, the car decelerates at a rate `beta` for time `(t - t_1)` and finally comes to rest. Then,
`0 = v - beta(t - t_1) rArr 0 = alpha t_1 - beta t + beta t_1`
`rArr t_1 = (beta)/(alpha + beta) t`
`:. v = (alpha beta)/(alpha + beta)t`.