A very large number of balls are thrown vertically upwards in quick successions in such a way that the next ball is thrown when the previous one is at the maximum height. If the maximum height is 5 m, the number of balls thrown per minute is (take g = 10 m/s2)
80
120
40
60
D.
60
A is the origin from where the ball is thrown.
Let u be the velocity of projection of ball.
∴ v2 = u2 − 2gh (upwards)
At B, v = 0
Ball is projected with 10 m/sec.
Time taken by ball to reach max height
v = u − gt
0 = 10 − 10t
⇒ t = 1 sec
In 1 sec, ball will reach the top and in next 1 sec it will reach the ground again.
∴ 1st ball reaches B in 1 sec.
IInd ball reached B in 1 sec.
When IInd is at B, 1st is at A and so on.
∴ Number of ball projected/sec = 1
Number of ball projected/min = 60
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120°
60°
90°
150°
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50 ms-1
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R/3
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20 %
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