Laws Of Motion Question 269
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 $ m{{s}^{-1}} $ . If the mass of each stone is $ 0.05kg $ what is the mass of the disc$ (g=10m{{s}^{-2}} $ ) [Kerala (Engg.) 2001]
Options:
A) $ 1.2kg $
B) $ 0.5kg $
C) $ 20kg $
D) 3kg
Show Answer
Answer:
Correct Answer: A
Solution:
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 $
therefore $ M=\frac{40\times 0.05\times 6}{10}=1.2kg $
