# Mastering physics :/

1. Mar 7, 2005

### RhysticGenesis

Ok here is the problem A hollow spherical shell with mass 2.50kg rolls without slipping down a slope that makes an angle of 30.0 degrees with the horizontal.
> Find the acceleration a_cm of the center of mass of the spherical shell.
> Take the free-fall acceleration to be g=9.80m/s^2.
> I got 24.2068 but again I was wrong

- I though it was mgsin(theta) was it not?

> Find the frictional force acting on the spherical shell.
Im not sure but wouldnt it be coefficient of friction (which I do not know) times the normal force (which would be the answer to the above I think?)

Another problem is :
A circular hoop of mass m, radius r, and infinitesimal thickness rolls without slipping down a ramp inclined at an angle theta with the horizontal. View Figure
> What is the acceleration a of the center of the hoop?
> Express the acceleration in terms of physical constants and all or some of the quantities m, r, and theta.

and to be honest I have no clue whatsoever on how to do that problem :/ man Im beginning to hate physics I dont understand it at all
:uhh:

2. Mar 7, 2005

### Erienion

Well, you know that the mass is 2.5 Kg, now find an equation to find I, the rotational inertia, given that all of the mass is in the spherical shell.