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