Two discs one of density 7.2 g/cm^(3) and the other of density 8.9 g/cm^(3) are of same mass and thickness. Their moments of inertia are in the ratio

Two discs one of density 7.2 g/cm^(3) and the other of density 8.9 g/c

1.	Two discs one of density 7.2 g/cm^(3) and the other of density 8.9 g/cm^(3) are of same mass and thickness. Their moments of inertia are in the ratio
Answer» `8.9 : 7.2` `7.2 : 8.9` `(8.9 xx 7.2) : 1` `1 : (8.9 xx 7.2)` Solution :`(I_(1))/(I_(2)) = ((1)/(2) M_(1) r_(1)^(2))/((1)/(2) M_(2 r_(2)^(2))) = (r_(1)^(2))/(r_(2)^(2))` As masses of two DISCS are equal , hence `(PI r_(1)^(2) t) rho_(1) = (pi r_(2)^(2) t) rho_(2)` or `(r_(1)^(2))/(r_(2)^(2)) = (rho_(2))/(rho_(1)) therefore (I_(1))/(I_(2)) = (rho_(2))/(rho_(1)) = (8.9)/(7.2)`