Mon June 11, 2012 By: Harshit

A ball is projected upwards from the foot of the tower. The ball crosses the tower twice after an interval of 6 sec and ball reaches the ground after 12 sec.What is the height of tower?

Expert Reply
Mon June 11, 2012
time taken to go uptoU and then come back to the ground required 12 sec.
So 6 s up then 6 s in coming down.
the time taken between climbing from T to U and then coming to T again(crossing T twice) =6 s
so time taken to go upto T from the ground=(12-6)/2=3s
now if we consider the journey from ground to U:
0=u-6x10 .......  putting in 1st eq.
u=60 m/s
now tower height:H=
H=60x3-1/2  x10x3x3.....putting in second eq
H=135 m
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