1. The problem statement, all variables and given/known data Question A disk is initially stationary on a platform. Force P is exerted on the platform. Mass of Disk is MD and Mass of Platform is MP. Determine the minimum coefficient of friction in order for the ball to not roll. What is the acceleration of the ball as seen from stationary frame? Attempt 2. Relevant equations F=ma I(alpha)=Summation of Moment 3. The attempt at a solution Acceleration of Ball has to be equal to the acceleration of the Platform since both starts from stationary. F (friction on ball)= MD x a P - F (friction on platform) = MP x a Since F can obtained, the angular acceleration of the ball is to be determined next. I x (alpha = angular acceleration) = (moment about center of the ball = Fr) With this "alpha" can be determined. Now for the last step, Acceleration of ball from neutral frame = acceleration of cart - (alpha x radius of ball) Hence, negative acceleration is obtained, which infer that the ball roll backwards. Please do correct me if there is any mistake. Thanks in advance.