9-47 in an elastic collision, a 400.0-kg bumper car collides directly from behind with a second, identical bumper car that is traveling in the same direction. the initial speed of the leading bumper car is 5.60 m/s and that of the trailing car is 6.00 m/s. assuming that the mass of the drivers is negligible, find the final speeds of both cars relative to the ground after the collision?