Question

We often use the centre of mass of the composite area to calculate the moment of inertia.  The centre of mass for these composite body is the ratio of ________ to _________

(a) The product of centroid and mass to the total weight

(b) The addition of centroid and weight to the total weight

(c) The subtraction of centroid and weight to the total weight

(d) The product of centroid and mass to the total mass

I had been asked this question by my school principal while I was bunking the class.

This intriguing question originated from Moment of Inertia for Composite Areas topic in division Moments of Inertia of Engineering Mechanics

Answer 1

Correct answer is (d) The product of centroid and mass to the total mass

To explain: The product of the centroid of the section to its mass to the total mass of the body is the centre of mass. Thus the answer. The ratio is generally used to locate the coordinate of the centroid or the centre of mass.