Question

Calculate the radius of the circular ring having a moment of inertia 59 kgm^2 and mass of  69 kg.

(a) .924 m

(b) .928 m

(c) .934 m

(d) .944 m

I had been asked this question in a job interview.

The doubt is from Modified Speed Torque Characteristics of DC Series Motors in division Characteristics of DC & AC Motors of Electric Drives

Answer 1

Correct answer is (a) .924 m

Easiest explanation: The moment of inertia of the circular ring can be calculated using the formula I=∑miri^2. The moment of inertia of a circular ring and mass is given. R=((59)÷(69))^.5 = .924 m. It depends upon the orientation of the rotational axis.