Question

A hockey puck of mass m slides over a frozen lake surface. It is thrown with the initial velocity v and slows down to zero velocity due to ice friction. A coyote from Arizona is sitting on the ice. From his point of view the initial kinetic energy is mv^2/2 and the final kinetic energy is 0. Thus the coyote concludes that the amount of energy dissipated through the ice friction is mv^2/2. At the same time a penguin flies from Pittsburgh with the velocity v in the direction opposite to the puck motion. From his point of view the initial velocity of the puck is 2v and the final velocity is v, so that the initial kinetic energy is m(2v)^2/2 = 2mv2 and the final kinetic energy is mv^2/2. Thus the penguin concludes that the amount of energy dissipated through ice friction is 3mv^2/2. Who is correct? Explain the origin and the size of the difference. (10 points)

Answer 1