Physicshard · Past Paper
A stone is dropped from a balloon rising upwards with a velocity of 12 m/s. If the balloon is at a height of 65m when the stone is dropped, how long will the stone take to reach the ground? (g=10 m/s^2)
A5 s
B13 s
C7 s
D3 s
✓ Correct Answer: A — 5 s
Use s = ut + 1/2 at^2 with s=-65, u=+12, a=-10. -65 = 12t - 5t^2 => 5t^2 - 12t - 65 = 0. Solving gives t = 5s.
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