Calculate the moment of inertia of this arrangement of masses. Each mass is located 2.5 m away from the axis. (You can envision the arrangement as a single rotating axis with four masses extending out from the axis like spokes of a wheel.)

Question

m1 is 1kg

m2 is 2kg

m3 is 3kg

m4 is 4kg

What formula for moment of inertia do I use? I was taking the sum of all values plugged into I = 4mr^2, but that was wrong. How do I find moment of inertia?

Thank you!

Answer 1

For a point-like mass, the moment of inertia about some axis is given by m r^2 For an extended rigid body, the moment of inertia is just the sum of all the small pieces of mass multiplied by the square of their distances from the axis in question. that does not total 4mr^2
unless you put in the 2.5 for radius.