Q39 of 176 Page 101

A stone falls from a building and reaches the ground 2.5 seconds later. How high is the building? (g = 9.8 m/s2)

Initial velocity, u=0m/s

Acceleration due to gravity, g=9.8m/s2


Time taken to reach the ground, t=2.5 sec


Height, h =?


Using relation, s = ut + gt2


s = 0 * 2.5 + * 9.8 * 2.5 * 2.5


s = 0 + 4.9 * 2.5 * 2.5


s = 30.625m


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A piece of stone is thrown vertically upwards. It reaches the maximum height in 3 seconds. If the acceleration of the stone be 9.8 m/s2 directed towards the ground, calculate the initial velocity of the stone with which it is thrown upwards.

 40

A stone is dropped from a height of 20 m.

(i) How long will it take to reach the ground?


(ii) What will be its speed when it hits the ground? (g = 10 m/s2)

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