Question

Calculate the mass of the ball having a moment of inertia 4.5 kgm^2 and radius of 14 cm.

(a) 229.59 kg

(b) 228.56 kg

(c) 228.54 kg

(d) 227.52 kg

The question was asked during an interview.

My doubt is from DC Motors Characteristics in section Characteristics of DC & AC Motors of Electric Drives

Answer 1

Correct option is (a) 229.59 kg

To explain I would say: The moment of inertia of the ball can be calculated using the formula I=∑miri^2. The moment of inertia of ball and radius is given. M=(4.5)÷(.14)^2 = 229.59 kg. It depends upon the orientation of the rotational axis.