Answer:
v = 10 [m/s].
Step-by-step explanation:
The largest mass is that of 4 [kg], in this way the momentum can be calculated by means of the product of the mass by velocity.
![P=m*v\\](https://img.qammunity.org/2022/formulas/physics/college/o67ewcfmdq4urk5r9g6m7v0jqtis37yssa.png)
where:
P = momentum [kg*m/s]
m = mass = 4 [kg]
v = velocity = 5 [m/s]
Now the momentum:
![P=4*5\\P=20[kg*m/s]](https://img.qammunity.org/2022/formulas/physics/college/najta4bx68feoqd256flc8uc0wvhsmkchn.png)
This same momentum is equal for the other mass, in this way we can find the velocity.
![P=m*v\\20=2*v\\v=10[m/s]](https://img.qammunity.org/2022/formulas/physics/college/w3kv87q8e0ptpf6q9tkuzptrc0ltl51f89.png)