Two Questions about Potential Energy

[Thefox14]

Homework Statement

If no non-conservative forces act on an object, which of the following values are constant for that object?

A. Its kinetic energy.
B. Its spring potential energy.
C. Its gravitational potential energy.
D. Its mechanical energy.


If an accelerating particle reaches a point where its total mechanical energy (Emech) is equal to its potential energy (U), then that particle is...

A. moving in the negative direction.
B. moving in the positive direction.
C. not moving.
D. moving with a negative mechanical energy with the subsystem of position.
E. moving with a negative mechanical energy with the subsystem of force.

2. The attempt at a solution

For question 1, I was thinking it would be A as the only forces acting on the object would be conservative forces but I'm not 100% sure.

As for question 2, I currently am thinking It's C because Emech = U + K, and since Emech is equal to U that would mean K is 0. Thus not moving. Is that correct?

 

[zhermes]

Good reasoning on '2,' you're right.

For question one, think of gravity for example (a conservative force), under the action of gravity, what is constant?

 

[Thefox14]

Hmm, well the gravitational potential energy would change in accordance to its height, but then that energy would be transferred to kinetic energy right? Oh, so then it would have to be D then.

 

[zhermes]

Exactly! ;)

 

[Thefox14]

Thanks!