A 4.0-kg mass is placed at (3.0, 4.0) m, and a 7.0 kg-mass is placed at (3.0, -.0) m. What is the moment of inertia of this system of masses about the z axis? A) 275 kg·m² B) 90 kg·m² C) 250 kg·m² D) 180 kg·m²

Question

Quizplus · Accepted Answer

The moment of inertia of a system of masses about an axis is the sum of the moments of inertia of the individual masses about that axis. The moment of inertia of a point mass m about an axis a distance r from the mass is mr^2. In this case, the moment of inertia of the 4.0-kg mass about the z axis is (4.0 kg)(3.0 m)^2 = 36.0 kg·m^2, and the moment of inertia of the 7.0-kg mass about the z axis is (7.0 kg)(4.0 m)^2 = 112.0 kg·m^2. Therefore, the total moment of inertia of the system of masses about the z axis is 36.0 kg·m^2 + 112.0 kg·m^2 = 148.0 kg·m^2.

A 40-Kg Mass Is Placed at (3