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Question
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?
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Solution
Here s = 20m, u = 0, a = 10 ms-2
We have, s = ut + `1/2` at2
∴ `(20) = 0 xx t + 1/2 (10)t^2`
⇒ `20 = 1/2 xx 10 t^2`
⇒ `(20 xx 2)/10 = t^2`
⇒ t2 = 4
∴ v = u + at
= 0 + 10 × 2
= 20 m s-1
The ball strikes the ground after 2 seconds with a velocity of 20 ms-1.
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