Eye Ahm Sofaking We Taught Ed: The Thread.

[Anonymous No.5301560]

Post anything that took you longer than it should have and ask questions.

My most recent one:
>Physics 1 homework because I wasn't on adderall/some other shenanigans and got set back two semesters of math
>(a)Find mass for moment of inertia given angular velocity, Kinetic Energy, radius, and the object (assumed) to be a hollow cylinder. (b) What would mass need to be were the cylinder solid?
>Nearly an hour later I give up and check Yahoo Answers
>I was supposed to do the second part first
>KE = 1/2(1/2 (M)(R)^2(Angular Velocity)^2 --> M = KE/(1/4 (R)^2(Angular V)^2
>All this arbitrary stuff about Inertia on various objects without explanation

Can someone please explain why (or derive mathematically) the mass of a hallowed cylinder is negligible enough to not be halved like a solid one is? Or maybe why the Inertia for a solid Sphere is 2/5ths of its mass by the square of its radius?

I suppose if nothing else I learned I should write problems in their entirety and use them all of them in their entirety. I started with just KE = (1/2(M)(R)^2)(Angular V)^2 and tried to solve for mass. Still don't know how to do that, but I'm almost positive it can be done.