First slide
Instantaneous acceleration
Question

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

Easy
Solution

v = U + at
30 = 20 + 5a a = 2 m/s2
v = at'
20 = 2t’      t’ = 10 sec when U = 0

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