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8. A ball dropped from a balloon at rest cltower 81 m high during the lastof its journey. Find the height of the alldand the velocity of the body when itthe ground.quarter secoreacheAns 2684.2 m 324 30

Answer»

The last quarter of the jouney means 1/4th of the total time it requires in its total journey.

Let total time be 4t, u = 0.

So, v at 3t = 3gt, and at 4t = 4gt.

by v² = u² + 2as,

16g²t² = 9g²t² + 2g(81)

7g²t² = 162g

7gt2= 162

t² = 162 / 7g

t = 1.5 sec.

but time is 4t = 6 sec.

So velocity on reaching = 4gt =58.8 m/s

With this velocity, height of fall = 2t(58.8) =705.6m



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