A gas balloon is going up with a constant velocity of 10 m/s. When this balloon reached a height of 75 m, a stone is dropped from it and balloon keeps moving up with the same velocity. The height of the balloon when the stone hits the ground is m. (Take g=10 m/s2)
- 85
- 150
- 129
- 125
Answer
(4) 125
Solution
At release the stone has the balloon's velocity, u = 10 m/s upward, at a height of 75 m. Taking upward as positive,
-75 = 10t - 12 10 t2
t2 - 2t - 15 = 0
(t - 5)(t + 3) = 0 t = 5 s
In these 5 s the balloon rises a further 10 5 = 50 m.
∴ Height of the balloon = 75 + 50 = 125 m
Answer: (4)