A stone of mass 10 kg has a rotational inertia of 2.4 kg · m² about an axis A parallel to an axis through the center of mass. If axis A is 0.20m from the center of mass axis, the rotational inertia about the center of mass axis is A) 0.40 kg · m² B) 2.0 kg · m² C) 2.4 kg · m² D) 2.8 kg · m² E) 4.4 kg · m²

Question

Quizplus · Accepted Answer

The parallel-axis theorem states that the rotational inertia of an object about an axis parallel to its center of mass axis is equal to the rotational inertia about the center of mass axis plus the product of the mass and the square of the distance between the two axes. 
Using the parallel-axis theorem, we can find the rotational inertia about the center of mass axis: 
Ic = Iparallel - md^2 
where Iparallel = 2.4 kg·m^2, m = 10 kg, and d = 0.20 m:

Ic = 2.4 kg·m^2 - (10 kg)(0.20 m)^2 = 2.0 kg·m^2

Therefore, the correct answer is B: 2.0 kg·m^2.

A Stone of Mass 10 Kg Has a Rotational Inertia