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Motion in Straight Line
Question
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From the foot of a tower 90m high, a stone is thrown up so as to just reach the top of the tower. Find the velocity with which the stone is thrown.

Answer

Height of the tower, h = 90 m 

Velocity of the stone when it reaches the top = 0 

Therefore, 

velocity, v = 0

acceleration, a = -9.8 m/s2

distance travelled, s = 90 m

Now, using the relation v2-u2 = 2as, we have 

02-u2 = 2x(-9.8) x 90

         = -1764
 
    u2 = 1764

      u = 42 m/s, is the velocity with which the stone is thrown. 

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