Concepts Of Physics MCQ Edition [Volume 1]PhysicsRotational Mechanics
Consider a body whose centre of mass is situated at the origin, with three of its particles located at (a, 0, 0) , (0, a, 0) , and (0, 0, a) . The moments of inertia of this body about the X and Y axes are each 0.20 kg-m ^2 . The moment of inertia about the Z -axis
Options
- Ais 0.40 kg-m ^2
- Bis 0.20 2 kg-m ^2
- Ccannot be deduced using the given information
- Dis 0.20 kg-m ^2
Correct answer
C. cannot be deduced using the given information
Step-by-step solution
The moments of inertia of a body about the X , Y , and Z axes are given by: I_x = m_i (y_i^2 + z_i^2) I_y = m_i (x_i^2 + z_i^2) I_z = m_i (x_i^2 + y_i^2) Adding the moments of inertia about the X and Y axes, we get: I_x + I_y = m_i (x_i^2 + y_i^2 + 2z_i^2) I_x + I_y = m_i (x_i^2 + y_i^2) + 2 m_i z_i^2 I_x + I_y = I_z + 2 m_i z_i^2 The perpendicular axis theorem, which states I_z = I_x + I_y , is only applicable for a two-dimensional planar body (lamina) lying entirely in the XY plane, where z_i = 0 for all particle