1. The problem statement, all variables and given/known data Two disks are mounted on a frictionless vertical shaft of neglible radius. The lower disk, of mass 440g and radius 3.5cm, is rotating at 180rpm on the frictionless shaft of neglible radius. The upper disk, of mass 270g and radius 2.3cm, is initially not rotating. It drops freely down the shaft onto the lower disk, and frictional forces act to bring the two disks to a common rotational speed. (a) What is that speed? (b) What fraction of the initial kinetic energy is lost to friction? 2. Relevant equations T = tau w= omega R = Radius m1 = mass lower disk m2 = mass upper disk I = rotational inertia = (1/2)mR^2 (for disks) upper disk = ud lower disk = ld alpha = angular acceleration a(tan) = tangential linear acceleration t=time Ok, i will just pop out some equations: T = I*alpha w = w0 + alpha*t a(tan) = alpha*R K(rotational) = (1/2)Iw^2 3. The attempt at a solution can we somehow use the K(rotational) equation to solve both? well first i converted (inital omega of the lower disk) w0(ld) 180rpm = 18.8 rad/s w0(ud) = 0 we know that wf(ud) = wf(ld) and we need to figure that out the m has to be in kg so --> m(ld) = 0.440kg m(ud) = 0.270kg Kf - Ki = deltaK lost from frictional force? (1/2)(m1 + m2)*wf^2 - (1/2)(m1)w0^2 = delta K lost? Any help would be great.