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4.1 , newtons laws of motion — Physics STD 11 Science — Question

Rajasthan BoardEnglish MediumSTD 11 SciencePhysics4.1 , newtons laws of motion1 Mark
MCQ
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  ........... $kg$     $(g = 10\,m{s^{ - 2}}$)
  • ✓
    $1.2$
  • B
    $0.5$
  • C
    $20$
  • D
    $3$
✓

Answer

Correct option: A.
$1.2$
a
(a)  Weight of the disc will be balanced by the force applied by the bullet on the disc in vertically upward direction.

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

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

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