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Question 7

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?

Answer

Distance covered by the ball, s = 20 m

Acceleration, a = 10 m/s2

Initially, velocity, u = 0 

Final velocity, v = ?

Time, t = ?

According to the third equation of motion:

v2 = u2 + 2 as

v2 = 0 + 2 (10) (20)

v = 20 m/s

According to the first equation of motion:

v = u + at

20 = 0 + 10 (t)

t = 2 s

Hence, time taken to reach at the ground is 2 seconds.

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