Q. Consider a circular disc of radius 20 cm with centre located at the origin. A circular hole of radius 5 cm is cut from this disc in such a way that the edge of the hole touches the edge of the disc. The distance of centre of mass of residual or remaining disc from the origin will be
A) 2.0 cm
B) 1.5 cm
C) 1.0 cm
D) 0.5 cm
Explanation
[Solution by Dr. Abubacker] The hole's centre is $15$ cm from the origin. Areas: hole $\propto25$, full disc $\propto400$, residual $\propto375$. $x_{cm}=-\frac{25\times15}{375}=-1.0$ cm, so the distance is 1.0 cm. Answer (3).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.