Question

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 $ms^{- 1}$. If the mass of each stone is $0.05kg$ what is the mass of the disc$(g = 10ms^{- 2}$)

• A. $1.2kg$
• B. $0.5kg$
• C. $20kg$
• D. 3kg

Answer 1

Answer: (A)

$1.2kg$

Answer 2

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

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

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