1. The problem statement, all variables and given/known data A uniform disc radius a, mass m there is rotation about an axis (z) tangental to the disc and in the plane of the disc. a point mass m is placed at the centre of the disc. what is the new moment about the axis z also show that the period of oscillations will decrease by SQRT(9/10) when the point mass is added 3. The attempt at a solution moment of inertia of just the disc i found to be = (5/4)ma^2 period before point mass added = T=2pi/w = 2pi*sqrt(m/k) torque = r x F = mga sin(theta) but we are told small angle approx applies so = mga*theta also F=k*theta so k = mga therefore T = 2pi*sqrt(m/mga) anf because of rotation the m on top = I about z axis so T = 2pi*sqrt(I/mga) = 2pi*sqrt(5a/4g) I dont know how to get the I when point mass has been added. also is the new torque = 2mga * theta so that k = 2mga ?