A solid ball of mass m and radius R is released from the position shown in a large hollow shell of same mass m and radius 3R as shown in figure. The displacement of the centre of mass of the system from its initial position when the solid ball ball touches the lower surface of the hollow shell is : (centres of both the spheres coincide intially) :

Options

A. 0
B. 3R
C. 2R
D. R

Answer

D

Explanation

Initially coordinate of centre of mass is (0,0)

When solid ball touches the lower surface of hollow surface
`V_("Cm)=(M(2R)+mx0)/(m+m)=R`
So finally coordinate of COM (0,R) displacement is (R-0) = R.