Question

Three identical spheres, each of mass $1kg$ are kept as shown in figure, touching each other, with their centres on a straight line. If their centres are marked $P,Q$ and $R$ respectively, the distance of centre of mass of the system from $P$ is :

• A. $\frac{PQ+PR+QR}{3}$
• B. $\frac{PQ+PR}{3}$
• C. $\frac{PQ+QR}{3}$
• D. $\frac{PR+QR}{2}$

Answer 1

The correct option is B $\frac{PQ+PR}{3}$

$r_1=0,r_2=PQ,r_3=PR$

Distance of centre of mass form $P$ is

$r=\frac{r_1+r_2+r_3}{3}$

$=\frac{0+PQ+PR}{3}$

$=\frac{PQ+PR}{3}$

Answer B: