A potter is spinning a pottery wheel that has a moment of inertia equal to 500 kg·m² and a radius of 2.0 m. It rotates at 2.50 rad/s and faces insignificant friction. Aiming toward the center of the spinning wheel, about which it rotates, the potter pushes some clay onto the edge of the wheel. This changes the wheel speed to 1.75 rad/s. Calculate the mass of the clay.