Question

Two disks are rotating about the same axis. Disk A has a moment of inertia of 3.1 kg · m2 and an angular velocity of +8.0 rad/s. Disk B is rotating with an angular velocity of -10.2 rad/s. The two disks are then linked together without the aid of any external torques, so that they rotate as a single unit with an angular velocity of -2.6 rad/s. The axis of rotation for this unit is the same as that for the separate disks. What is the moment of inertia of disk B?

The negative signs are confusing me.

Answer 1

I w before = I w after by conservation of angular momentum

3.1 * 8 - 10.2 * I = -2.6 (3.1+I)

Answer 2

Thanks!

Answer 3

You are welcome.

Answer 4

How would one go about simplifying that equation down to an answer? I'm stumped by it for some reason.