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]

• A.             \[1.2kg\]          
• B.             \[0.5kg\]
• C.             \[20kg\]           
• D.             3kg