a person with mass m stands at the outer edge of a round platform whose radius is r and whose mass is m2. the platform is rotating at a speed of ...rad/s. Assuming the platform to be a free rotating disk, what would be its angular speed if the person walked to its center? Then the answer book says.... L(i) = L(f) because sum(torque) = 0... How would I know the sum of the torques is zero...? Is the paragraph said.. " Assuming the platform to be a free rotating disk..." ?