Posted by Anonymous on Wednesday, July 28, 2010 at 11:09am.
The rigid object shown in Fig. 1063 consists of three balls and three connecting rods, with M = 1.5 kg, L = 0.67 m, and θ = 32°. The balls may be treated as particles, and the connecting rods have negligible mass. Determine the rotational kinetic energy of the object if it has an angular speed of 1.2 rad/s about
(a) an axis that passes through point P and is perpendicular to the plane of the figure, and
(b) an axis that passes through point P, is perpendicular to the rod of length 2L, and lies in the plane of the figure.
The figure shows a point P, then to the left of that point is a ball of mass 2M connected by a rod length L at an angle theta degrees from the horizontal. There is another mass 2M ball that is connected by a rod of length L at negative theta to the horizontal. To the right of point P there is a ball of mass M connected by a rod of length 2L.
So far, I have the formula K.5Iw2, but I don't know how to find I for this system of particles. Any help would be much appreciated

Physics  bobpursley, Wednesday, July 28, 2010 at 11:24am
The system moment of inertia will be the sum of all three. If the masses are the same, and the lengths the same, 3/2mr^2 will be total. Remember, when you derived the moment of inertia, you integrated (summed) all point masses at some distance r from the rotation.

Physics  Anonymous, Wednesday, July 28, 2010 at 9:56pm
Okay so I got the first part alright, but then when the axis of rotation changes, would that affect I?
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