Q.

A uniform circular disc of radius a is taken. A circular portion of radius b has been removed from it as shown in the figure. If the centre of hole is at a distance c from the centre of the disc, the distance x2 of the centre of mass of the remaining part from the initial centre of mass O is given by

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a

πb2(a2-c2)

b

cb2(a2-b2)

c

πc2(a2-b2)

d

ca2(c2-b2)

answer is B.

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Detailed Solution

Consider the mass of the removed portion as negative.

Mass of original disc=M=σπa2

Mass of removed portion =-m=-σπb2

Position of centre of mass = M.xM+(-m)xmM-m

xc.o.m=-σπb2.cσπa2-σπb2=cb2a2-b2

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A uniform circular disc of radius a is taken. A circular portion of radius b has been removed from it as shown in the figure. If the centre of hole is at a distance c from the centre of the disc, the distance x2 of the centre of mass of the remaining part from the initial centre of mass O is given by