Is Momentum Conserved with Different Force Directions and Types?

[dherm56]

5) If there are no external forces acting on a system in the x direction, but there is an external force acting on the system in the y direction, then the y component of momentum of the system is constant.

True
False

6) If work is done on an object by only conservative forces, then the momentum of that object must be conserved.

True
False

7) The Work-Kinetic Energy theorem is invalid if work is done by a non-conservative force.

True
False

I answered False, True, True.
any sugestions?

 

[Astronuc]

How about showing one's reasoning.