Question

Consider two perpendicular axis in the plane of a planar body, such that I1 = 2 I2. The moment of inertia about an axis perpendicular to the plane and passing through intersection of I1 & I2 is 9kgm^2. Find the value of I1& I2.

(a) I1 = 9kg m^2, I2 = 4.5kgm^2

(b) I1 = 3kg m^2, I2 = 6kg m^2

(c) I1 = 6kg m^2, I2 = 3kg m^2

(d) I1 = 18kg m^2, I2 = 9kg m^2

This question was addressed to me in semester exam.

This key question is from Theorems of Perpendicular and Parallel Axes in section System of Particles and Rotational Motion of Physics – Class 11

Answer 1

Right option is (c) I1 = 6kg m^2, I2 = 3kg m^2

The explanation: By perpendicular axis theorem:                                                                                                                              9 = I1 + I2 = 3 I2.

∴ I2 = 3kgm^2 & I1 = 2*3 = 6kgm^2.