Question

# A ball thrown vertically upwards with a speed of 19.6 m/s from the top of a tower returns to the earth in 6s. Find the height of tower :

A

60

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B

58

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C

58.8

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D

None of these

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Solution

## The correct option is C. 58.8 m.Let the height of the tower be h. Here, u=19.6 m/s t=6 s s=−h (The magnitude of the displacement is the height of the tower. Since it is in the direction opposite to the initial velocity, its negative value is taken). a=−g=−9.8 m/s2 (It is taken as negative because the direction of acceleration due to gravity is downwards, while the initial velocity is upwards).Using the second equation of motion s=ut+12at2 we get, ∴−h=(19.6×6)−9.8 × 6 × 62 =−58.8 m Thus, the height of the tower is 58.8 m.

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