Question

Calculate the moment of inertia of the thin spherical shell having a mass of 73 kg and diameter of 36 cm.

(a) 1.56 kgm^2

(b) 1.47 kgm^2

(c) 1.38 kgm^2

(d) 1.48 kgm^2

This question was addressed to me in a national level competition.

The query is from DC Motors topic in section Characteristics of DC & AC Motors of Electric Drives

Answer 1

The correct choice is (a) 1.56 kgm^2

Easy explanation: The moment of inertia of the thin spherical shell can be calculated using the formula I=mr^2×.66. The mass of the thin spherical shell and diameter is given. I=(73)×.66×(.18)^2=1.56 kgm^2. It depends upon the orientation of the rotational axis.