A ball of mass 400 gm is dropped from a height of 5 m. A boy on the ground hits the ball vertically upwards with a bat with an average force of 100 N so that it attains a vertical height of 20 m. The time for which the ball remains in contact with the bat is [g = 10 m/s2]
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a
0.12 s
b
0.08 s
c
0.04 s
d
12 s
answer is A.
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Detailed Solution
Velocity by which the ball hits the batv1 = 2gh1 = 2×10×5 or v1 → = +10 m/s = 10 m/sVelocity of reboundv2 = 2gh2 = 2×10×20 = 20 m/s or v2→ = -20 m/sF = mdvdt = m(v2→ - v1)dt = 0.4(-20-10)dt = 100 Nby solving, dt = 0.12 sec