A metal plate weighing 200g is balanced in mid air by throwing 40 balls per second vertically upward from below. After collision, balls rebound with the same speed. What is the speed with which the balls strike the plate? [Given : mass of each ball = 200g and g = 10m/s^2 ]
(1) 5.7 cm/s
(2) 12.5 cm/s
(3) 9.8 cm/s
(4) 14 cm/s
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EXPLANATION.
- GIVEN
a metal plate weight 200 g is balanced in the
mid air by throwing 40 balls per second.
TO FIND THE SPEED WITH WHICH THE BALLS STRIKE THE PLATE.
according to the question,
weight of plate = force exerted by 40 balls per
second.
weight of plate = w = mg
Force exerted by 40 balls per second is =
F = 40 X ma = 40 X mv / t [ where t = 1 seconds ]
F = 40 X ma = 40 X mv
Therefore,
acceleration = g = 10 m/s^2
mg = mv
Let,
mass of plate = 200g = 0.2 kg
mass of ball = 200g = 0.2 kg
0.2 X 10 = 40 X 0.2 X v
v = 10 / 40
v = 0.25 m/s
Therefore,
velocity of each ball = 0.25 m/s
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