A circular disc of radius R is removed from a bigger circular disc of radius 2R, such that the circumference of the disc coincides. The centre of mass of the new disc is αR from the centre of bigger disc. The value of alpha is

A circular disc of radius R is removed from a bigger circular disc of

1.	A circular disc of radius R is removed from a bigger circular disc of radius 2R, such that the circumference of the disc coincides. The centre of mass of the new disc is αR from the centre of bigger disc. The value of alpha is
Answer» `1/3` `1/2` `1/6` `1/4` Solution :MASS of original DISC = m Mass of disc removed, `m_(1) = m/4` Mass of remaining disc `=(3m)/4` Mass `m_(1)` and `m_(2)` are concentrated at `O_(1)` and `O_(2)` respectively and O is their centre of mass. Moment of `m_(1)` about O = moment of `m_(2)` about O. `m/4 xx R = (3m)/R xx ALPHA R RARR alpha =1/3`