A solid disc of mass M is just held in air horizontally by throwing 40 stones per sec vertically upw

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4-1.Newton's Laws of Motion

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A solid disc of mass $M$ is just held in air horizontally by throwing $40$ stones per sec vertically upwards to strike the disc each with a velocity $6\,m{s^{ - 1}}$. If the mass of each stone is $0.05\,kg$ what is the mass of the disc ........... $kg$ $(g = 10\,m{s^{ - 2}}$)

A

$1.2$

B

$0.5$

C

$20$

D

$3$

Solution

(a) Weight of the disc will be balanced by the force applied by the bullet on the disc in vertically upward direction.

$F = nmv = 40 \times 0.05 \times 6 = Mg$

$⇒$ $M = \frac{{40 \times 0.05 \times 6}}{{10}} = 1.2\,kg$

Standard 11

Physics

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