Q11 of 23 Page 117

A ball is dropped from a balloon going up at a speed of 5 m/s. If the balloon was at a height 60 m. at the time of dropping the ball, how long will the ball take to reach the ground?

According to question it is given;

Speed of balloon = 5m/s (upward)


⇒ Velocity of ball (u) = -5 m/s (because ball will fall downwards)


Height (S) = 60 m


Time to reach ground (t) = ?


By newton’s second equation of motion


Distance (S) = ut +


⇒ 60 = -5t +


⇒ 60 = -5t + 5t2.


⇒ = -t + t2.


⇒ 12 = -t + t2.


⇒ t2 – t – 12 = 0;


⇒ (t – 4) (t – 3) = 0;


⇒ t = 4, -3;


But time can’t be negative;


∴ t = 4 s


Hence Time taken by the ball to reach the ground is 4 s


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