KinematicsMedium
Question
A ball is dropped from a bridge 122.5m high. After the ball has fallen for 2 second, a second ball is thrown straight down after it. what must be the velocity of second ball so that both the balls hit the surface of water at the same time?
Options
A.26.1m/s
B.9.8m/s
C.55.5m/s
D.49m/s
Solution
Time takn by the first object to reach the ground = t, so
122.5 = ut +
gt2
122.5 = × 10 × t2
⇒ t = 5 sec (approx)
Time to be taken by the second ball to reach the ground = 5 - 2 = 3 sec. Ifu be initial velocity then,
122.5 = u × 3 +gt3 = 3u + × 10 × 9
3u = 122.5 - 45 = 77.5
u = 26 (approx.)
122.5 = ut +
gt2122.5 =
× 10 × t2 ⇒ t = 5 sec (approx)
Time to be taken by the second ball to reach the ground = 5 - 2 = 3 sec. Ifu be initial velocity then,
122.5 = u × 3 +
gt3 = 3u + × 10 × 93u = 122.5 - 45 = 77.5
u = 26 (approx.)
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