A ball is gently dropped from a height of 20 m. If its velocity increases uniformly at the rate of 10 m s-2, with what velocity will it strike the ground? After what time will it strike the ground?
Given,
Initial velocity, u = 0 (As the ball is dropped from rest)
Final velocity, v =?
Acceleration, a = 10 m/s2
Distance, s = 20 m
We know that,
v2 = u2 + 2as
v2 = (0)2 + 2 × 10 × 20
v2 = 0 + 400
v2 = 400
v = 
v = 20 m/s
Now we have to calculate the time taken:
We know that:
v = u + at
20 = 0 + 10 × t
10t = 20
t = 
t = 2 s
Therefore, after 2 seconds the ball will strike the ground.
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