From a uniform circular disc of radius 20 cm, a circular portion of radius 5 cm is removed internally so that the small circle is tangent to the outer circumference. The magnitude of shift of the centre of mass is:

Question

G1 Physics · Accepted Answer

Removed mass is proportional to area: m=M(5²/20²)=M/16. Its centre is 20-5=15 cm from the original centre. Treating the removed part as negative mass, |x|=[(M/16)15]/(M-M/16)=15/15=1 cm.