MEDAL GIVEN TO CORRECT ANSWER.
Two hockey pucks with mass 0.1 kg slide across the ice and collide. Before the collision, puck 1 is going 8 m/s to the east and puck 2 is going 7 m/s to the west. After the collision, puck 1 is going 7 m/s to the west. What is the velocity of puck 2?

A. 7 m/s east
B. 8 m/s west
C. 8 m/s east
D. 7 m/s west

Question

MEDAL GIVEN TO CORRECT ANSWER. 
Two hockey pucks with mass 0.1 kg slide across the ice and collide. Before the collision, puck 1 is going 8 m/s to the east and puck 2 is going 7 m/s to the west. After the collision, puck 1 is going 7 m/s to the west. What is the velocity of puck 2?

 		A.	7 m/s east
 		B.	8 m/s west
 		C.	8 m/s east
 		D.	7 m/s west

anonymous · Answer

8 m/s East

anonymous · Answer

Define East as positive and West as negative. Momentum before is 0.1kgm/s. Momentum after is -0.7kgm/s +0.1 V, where V is the desired velocity. Bring the -0.7kgm/s over to left hand side to get 0.8kgm/s, divide by the 0.1 from the right hand side to find V to be 8m/s in the positive direction, East

anonymous · Answer

Since the ice is friction-less no net external force acts on the '2 puck system'.So momentum is conserved .Now equate the initial momentum and final momentum .