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CBSE Class 9 Answered

A ball is gently dropped from a height of 20m. If its velocity increases uniformly at the rate of 10m/s2  then with what velocity will it strike the ground? After what time will it strike the ground?
Asked by Topperlearning User | 16 Jun, 2016, 05:37: PM
answered-by-expert Expert Answer

Initial velocity, u = 0 (dropped gently); Acceleration, a = 10 m/s2

Height, s = 20 m; Final velocity, v =? And Time taken, t =?
 
Use third equation of motion:

begin mathsize 12px style straight v squared equals straight u squared plus 2 as rightwards arrow straight v squared equals 0 plus 2 cross times 10 cross times 20 rightwards arrow straight v squared equals 400 rightwards arrow straight v equals 20 space straight m divided by straight s Using space the space second space equation space of space motion comma space we space get straight s equals ut plus 1 half at squared rightwards arrow 20 equals 0 cross times straight t plus 1 half cross times 10 cross times straight t squared rightwards arrow straight t squared equals 4 rightwards arrow straight t equals 2 space straight s end style

Answered by | 16 Jun, 2016, 07:37: PM

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