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A ball is dropped from a ballon going up...

A ball is dropped from a ballon going up at a speed of 7 m/s. If the balloon was at a height 60 m at the time of dropping the ball, how long will the ball take in reaching the ground?

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The correct Answer is:
A, B, C
Initially the ball is going upward `u=-7 m/s
S=60
a= g= 10 m/s^2
From S=ut+1/2 at^2
60=-7t+1/2 10 t^2
rarr 60=-7t+5t^2
rarr5t^2-7t-60=
:. T=(7+-(sqrt(49+1200)))/(2xx5)
=(7+-(sqrt(49+1200)))/1
=(-7+-35.34)/10
Taking +ve sign
t= (7+35.34)/10=4.2 sec`
Therefore, the ball will take 4.2 sec, to reach the ground.
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