Question

A uniform disc of radius R put over another uniform disc of radius 2R of same thickness and density, the peripheries of the two discs touch each other. The position of their centre of mass is

• A. at $\frac{R}{3}$ from the center of bigger disc towards the center of the smaller disc
• B. at $\frac{R}{5}$ from the center of the bigger disc towards the center of the smaller disc
• C. at $\frac{2R}{5}$ from the center of the bigger disc towards the center of the smaller disc
• D. at $\frac{2R}{5}$ from the center of the smaller disc

Answer 1

Answer: (B)

Distance of C.M. from centre of big disc
$x = \frac{r^2 a}{R^2 +r^2}$
r- radius of small disc
R- radius of big disc
a- distance between the centres of discs