Momentum and kinetic energy questions

[celee2]

[SOLVED] Momentum and kinetic energy questions

Homework Statement

4) 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 x component of momentum of the system is constant.

True
False

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

True
False

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

True
False

Homework Equations

The Attempt at a Solution

true/false questions about conservation of kinetic energy and momentums...
I don't think I got the concept of the whole conservation thing...
any help would be appreciated:]

 

[jambaugh]

Get out your textbook and read it. Use the index to look up references to the various terms you don't understand.

These questions are so direct that there's not much "hinting" one can do without actually giving the answers. You need to integrate the definitions into your thinking so that the answers become obvious to you.

But here are some general points. A conservative force is a force that conserves some quantity when acting over a closed path. You go around a loop and something in particular doesn't change. As to which quantity you'll have to look that up.

A quantity is conserved when it doesn't change under the dynamic evolution of the particular system. Different dynamics (i.e. different types of forces) and you'll have different quantities being conserved or not conserved.

Beyond that . . . all I can tell you is to read your textbook. If it's not the best at explaining find a library and check out another book on introductory Physics or Google around and you should be able to find a website explaining the various concepts.

 

[Moetasim]

I would like to clarify the concepts of momentum and kinetic energy in relation to these questions. Momentum is the product of an object's mass and its velocity, and it is a measure of the object's motion. In a closed system where there are no external forces acting, the total momentum remains constant. This means that the x component of momentum will also be constant, regardless of any external forces acting in the y direction. Therefore, the statement is true.

Regarding the second question, the conservation of momentum and the conservation of kinetic energy are two separate concepts. While the conservation of momentum states that the total momentum of a closed system remains constant, the conservation of kinetic energy states that the total kinetic energy of a closed system remains constant. It is possible for the momentum of an object to be conserved while its kinetic energy is not, and vice versa. Therefore, the statement is false.

Finally, the Work-Kinetic Energy theorem states that the net work done on an object is equal to the change in its kinetic energy. This theorem is valid for both conservative and non-conservative forces. However, if work is done by a non-conservative force, the change in the object's kinetic energy will not be equal to the work done, as some of the energy will be lost to other forms. Therefore, the statement is false.

I hope this explanation helps in understanding the concepts of momentum and kinetic energy better. If you have any further questions or concerns, please do not hesitate to ask.