Answer :
Given
M = 56 kg
m = 31 kg
vm = 1.96m/s
Procedure
The law of momentum conservation can be stated as follows. For a collision occurring between object 1 and object 2 in an isolated system, the total momentum of the two objects before the collision is equal to the total momentum of the two objects after the collision.
[tex]\begin{gathered} m*v_{om}+M*v_{oM}=m*v_{fm}+M*v_{fM} \\ 0=mv_{fm}+Mv_{fM} \\ 0=31*1.96m/s+56*v_{fM} \\ v_{fM}=\frac{-31*1.96m/s}{56} \\ v_{fM}=-1.085m/s \end{gathered}[/tex]
Martin's final velocity is -1.085 m/s