Q.
Three identical spheres, each of mass 1 kg are kept as shown in figure below, touching each other, with their centers on a straight line. If their centres are marked $P$, $Q$, $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) $\frac{PR + QR}{3}$
Explanation
(b) $r_{1} = 0,\ r_{2} = PQ,\ r_{3} = PR$
Distance of centre of mass from $P$ is
$r = \frac{r_{1} + r_{2} + r_{3}}{3} = \frac{0 + PQ + PR}{3} = \frac{PQ + PR}{3}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.