Mechanical Energy: Kinetic & Potential Energy Balance

[wolves5]

1. The total mechanical energy of a system:

a. is split equally between kinetic energy and gravitational potential energy.
b. is constant as long as only conservative forces act on it.
c. is either only kinetic energy or only gravitational potential energy at any given time.
d. cannot be determined for most naturally occurring systems.

For this question, I think the answer is A. This is because Total Mechanical Energy is eqaul to Potential Energy + Kinetic Energy. Is my reasoning right?

 

[gneill]

So, you're proposing that KE is always equal to PE?

 

[wolves5]

Yes..isnt that right?

 

[gneill]

In all the projectile problems that you've worked on, was potential energy always (at all times) equal to kinetic energy? Even, for example, when a vertically launched projectile is at the top of its trajectory?

 

[wolves5]

Oh no it wasnt the same. So since its not split equally, it would be C then?

 

[gneill]

Oh no it wasnt the same. So since its not split equally, it would be C then?

I think that you should reflect on the problems that you've done involving PE and KE and try to draw logical arguments for accepting or rejecting the provided choices. Remember, a single counterexample disproves a proposition.

I'm not going to answer your question for you by eliminating or confirming them one at a time when you say something like, "Is it C?"