The velocity of a body at an instant is 20 ms–1. After 5s the velocity is 30 ms–1. How many seconds earlier from the instant, it might have started? Assume acceleration is uniform
v = U + at
30 = 20 + 5a a = 2 m/s2
v = at'
20 = 2t’ t’ = 10 sec when U = 0