A 4.0-n puck is traveling at 3.0 m/s. it strikes an 8.0-n puck, which is stationary. the two pucks stick together. their common final speed is:

1.0 m/s Momentum = mass x velocity Total Momentum before any collision = total momentum afterwards 4.0 x 3.0 = 12 : g x momentum before (x g because using weight) Afterwards, if the velocity of the two joined is v then we get: 'momentum x g'=12v so 12v=12 so v=1m/s