Using conservation of momentum:
[tex]\begin{gathered} p1=p2 \\ p1=m1u1+m2v1 \\ p2=m1u2+m2v2 \end{gathered}[/tex]Where:
m1 = mass of the hockey puck 1 = m2 = mass of the hockey puck 2 = 0.1kg
u1 = Initial speed of the hockey puck 1 = 13m/s
u2 = Final speed of the hockey puck 1 = 18m/s
v1 = Initial speed of the hockey puck 2 = 18m/s
v2 = Final speed of the hockey puck 2
Therefore:
[tex]\begin{gathered} 0.1(13)+0.1(18)=0.1(18)+0.1v2 \\ 13+18=18+v2 \\ solve_{\text{ }}for_{\text{ }}v2: \\ v2=13+18-18 \\ v2=13m/s \end{gathered}[/tex]Answer:
13 m/s