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# A ball is dropped from a balloon 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

Asked by gargpuneet989 19th July 2018, 2:50 PM
The equation to be used for solving this question is " S = u×t - (1/2)×g×t2 " ,

where S is the overall disance to be travelled before hitting the ground,
here S = -60 m because to hit the ground from the point of dropping the stone has to travel 60 m in opposite direction.
u is initial speed , here u = 7 m/s in vertical direction because at the time of dropping the stone balloon moves upward 7 m/s.
t is time in seconds.

substituting the relevant values in the above equation we get, -60 = 7×t -(1/2)×9.8×t2 or  4.9t2 - 7t - 60 = 0  ..........(2)

by solving the quadratic equation (2), we get t = 4.3 s
Answered by Expert 19th July 2018, 6:46 PM
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