A ball is thrown vertically upwards from a tower with a velocity 20 m/s. The ball strikes theearth after 5 sec of trowing. What is the height of the tower? What will be the velocity of ball while stroking the earth? (g=9.8m/s2)

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Solution

Let us suppose the total height of the tower=h
and hence by applying the equation of motion
s=ut+1/2atsquare
By substituting the values u=20 a=-g and t=5
-h=205+1/2(-9.855)
(taking upward as positive and downward as negative)
-h=100+1/2-9.855
=100-(245/2)
=100-122.5
=-22.5

-h=-22.5
so h=22.5
Height of the tower=22.5m.

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