Puck 1 of known mass m, is sent sliding across a frictionless lab bench, to undergo a one- dimensional elastic (i.e. kinetic energy is conserved) collision with a stationary puck 2. Puck 2 then slides off the bench and lands a distance d from the base of the bench. Puck 1 rebounds from the collision and slides off the opposite edge of the bench, landing a distance 2d from the base of the bench. What is the mass of puck 2?