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.

 

[nlightner]

Your answers are correct. Here are some explanations for each statement:

5) This statement is true because according to the law of conservation of momentum, the total momentum of a system remains constant in the absence of external forces. Since there are no external forces acting on the system in the x direction, the x component of momentum will be constant. However, the y component of momentum may change due to the external force acting on it.

6) This statement is also true because conservative forces are those that do not depend on the path taken by the object. Therefore, the work done by these forces does not change the object's kinetic energy, and hence, its momentum remains constant.

7) This statement is also true because the Work-Kinetic Energy theorem states that the net work done on an object is equal to the change in its kinetic energy. However, if a non-conservative force is doing work on the object, the work done may not result in a change in kinetic energy. Therefore, the theorem is not valid in this scenario.