Potential energy greater total energy in the system?

[shredder666]

First of all this is not a HW question, I already "handed" the assignment in and its graded

There was this question on my assignment, it asked questions off of a graph that had distance on the x-axis and energy on the y axis.
The potential energy was a curve, and basically took up the entire page.
the total energy was just a horizontal line and intercepts the PE curve at several points.

But the strange thing was that the TE line was below the PE curve at several intervals. Which just totally confuse me, cus the potential energy is greater than the total energy... or is that some sort of convention that i don't know about

 

[Gordianus]

From a classical point of view, the movement of the object is restricted to the zone where total energy is less than potential energy.
The other regions are "forbidden" in the sense that, within those zones, the kinetic energy is less tan zero and it would lead to an imaginary speed.
QM predicts another behavior, but I think you're looking for a "classical" answer

 

[shredder666]

yes, I am looking an answer that does not involve the word "quantum".
So I don't get why that portion is there, is it some sort of bad question making?

 

[aim1732]

The potential energy is a function eg. the potential energy for a linear simple harmonic oscillator is 1/2kx²---the function is real for all real x---- but there are constraints on x put by limits of total energy. But the potential energy is still a function and it can have the corresponding value for an x that gives an imaginary speed----if that were possible.

 

[bp_psy]

But the strange thing was that the TE line was below the PE curve at several intervals. Which just totally confuse me, cus the potential energy is greater than the total energy... or is that some sort of convention that i don't know about

For gravitational potential energy the potential energy function is liner U=mgh. It can get negative.In order to lift something at point p1 that is below your reference point at O set to 0 you must do work w=-mgh(h distance from p1 to O).Since gravitation is a conservative force and you are measuring with respect to some point the increase in Kinetic energy from O to p1 is equal to w so your total energy will be unchanged.No problems and no quantums.For a spring this is not possible since U=(1/2)kx^2 so if you get -U there is a problem..