In a football game, a receiver is standing still, having just caught a pass. before he can move, a tackler, running at a velocity of +4.1 m/s, grabs him. the tackler holds onto the receiver, and the two move off together with a velocity of 2.1m/s. the mass of the tackler is 105 kg. assuming that the momentum is conserved, find the mass of the receiver. what is the average force on the receiver if in contact for 1 second? what is the average force on the tackler if in contact for 1 second?