The question I'm having trouble with is: A child of mass 28.0 kg is sliding on ice with a velocity of 2.25 m/s in the positive x direction. She is holding a 2.4 kg ball in her hand. She throws the ball straight ahead of her with a velocity of 2.70 m/s (in the x direction). What is her velocity immediately after releasing the ball? I think I need to get the rotational inertia for the ball to get its kinetic energy but i'm not given a radius.