# Analytic expressions of the kinetic and potential energy [closed] A homogeneous rigid circular disc (radius R, mass ms, center point S) rolls without a slip on a plain with a small angle of inclination alpha against the horizontal. A point mass MG is fixed on the disc in a distance e to the center point S. The motion of the disc can be described by the angle phi between the vertical and the connection line SMG.

Please see the figure for reference.

I am trying to calculate Kinetic Energy and Potential energy of the given problem (pic #2) and I have considered both masses as one system but I am not sure if that's correct or not. Also, I am not sure if the h term in potential energy (mgh) is correct here. So I would be glad if someone could throw some light on this. Thanks in advance!

• This is an obvious homework problem, and further is a Physics question, not Engineering. – Carl Witthoft Aug 10 '18 at 17:25 • $p_g$ is the sum of vectors $p_s$ and the position $\{e \sin (\alpha ),-e \cos (\alpha )\}$ of $MG$ w.r.t the center of $Ms$. The latter is in a different coordinate system that rotates with the $Ms$. Hence the rotation matrix to get both in the same coordinate system. – Suba Thomas Aug 13 '18 at 13:49