- #1
Phan
- 32
- 0
Technically, I don't really have a problem specifically that I need help on solving, but there is a crucial concept that I cannot grasp about the WET, and until I can do so, most WET problems are a pain to me.
My professor gave us two types of formulas for the work energy theorem, stating that there are more and each will get progressively better and designed for use on more situations. The first one we got, and the one most high school students receive, is:
W = delta (K),
where W is work and the RHS is the change in kinetic energy.
The second equation is:
Wnc = (delta K) + (delta Ug) + (delta Us),
where Wnc is non conservative work, Ug is gravitational work, and Us is spring work.
Since the professor really only gave one example for each theorem, I decided to take the liberty and try several more textbook questions. From what I have found out, the first theorem could be used for almost any of the problems that I encountered, as I could keep putting in different forces:
ex. Delta K = Wg + Ws + Wa
From my understanding, the work for the first equation means conservative work, which I suppose means that work with a constant force. The thing is, the individual values of W that I have used in various equations are non-conservative at times, such as the work of a spring.
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If this is the case, why is the second equation used for situations where there is no friction (my professor did an example like that in class)? Furthermore, how does one use the second theorem? This is a question that my professor has given:
A 100kg car goes up a 10deegree hill at a constant a. Starts at 10m/s, travels 2km, the final speed is 2.5m/s. There is slipping, creating a frictional energy of 2120kG, what is the energy expended by the car?.
What was done was that the Wnc (or LHS) was set to Wapp - Wfric, both of which are non-conservative forces. So, if this is the case, why is the general equation not set so that the Spring Force (Us) is taken out and included on the Wnc side?
I believe that my hopelessness is a result of my weak physics background, and I am thus confused by these two equations in general. When should I use theorem #1 or theorem#2, and how do they differ specifically?
Finally, a non-conservative force is one in which the start and end point doesn't matter or is not path dependent (ala force is constant), whereas a conservative force is one in which the path taken is taken into account (force is variable)? I am not sure if I am correct about these two ideas, since they seem critical to the understanding of the theorems stated earlier.
It is Thanksgiving Weekend and my professor has gone home, I didn't intend to ask him about these concepts since I thought I could grasp them after re-reading my notes, but 2hours of various problems and internet searching has not helped at all. Any help here would be appreciated D:
PS. For whoever that answered my Bosun question, I appreciate your help. I'm too lazy to dig up the thread and reply to it, so know that I genuinely benefited from your post :D
My professor gave us two types of formulas for the work energy theorem, stating that there are more and each will get progressively better and designed for use on more situations. The first one we got, and the one most high school students receive, is:
W = delta (K),
where W is work and the RHS is the change in kinetic energy.
The second equation is:
Wnc = (delta K) + (delta Ug) + (delta Us),
where Wnc is non conservative work, Ug is gravitational work, and Us is spring work.
Since the professor really only gave one example for each theorem, I decided to take the liberty and try several more textbook questions. From what I have found out, the first theorem could be used for almost any of the problems that I encountered, as I could keep putting in different forces:
ex. Delta K = Wg + Ws + Wa
From my understanding, the work for the first equation means conservative work, which I suppose means that work with a constant force. The thing is, the individual values of W that I have used in various equations are non-conservative at times, such as the work of a spring.
_____________________________________
If this is the case, why is the second equation used for situations where there is no friction (my professor did an example like that in class)? Furthermore, how does one use the second theorem? This is a question that my professor has given:
A 100kg car goes up a 10deegree hill at a constant a. Starts at 10m/s, travels 2km, the final speed is 2.5m/s. There is slipping, creating a frictional energy of 2120kG, what is the energy expended by the car?.
What was done was that the Wnc (or LHS) was set to Wapp - Wfric, both of which are non-conservative forces. So, if this is the case, why is the general equation not set so that the Spring Force (Us) is taken out and included on the Wnc side?
I believe that my hopelessness is a result of my weak physics background, and I am thus confused by these two equations in general. When should I use theorem #1 or theorem#2, and how do they differ specifically?
Finally, a non-conservative force is one in which the start and end point doesn't matter or is not path dependent (ala force is constant), whereas a conservative force is one in which the path taken is taken into account (force is variable)? I am not sure if I am correct about these two ideas, since they seem critical to the understanding of the theorems stated earlier.
It is Thanksgiving Weekend and my professor has gone home, I didn't intend to ask him about these concepts since I thought I could grasp them after re-reading my notes, but 2hours of various problems and internet searching has not helped at all. Any help here would be appreciated D:
PS. For whoever that answered my Bosun question, I appreciate your help. I'm too lazy to dig up the thread and reply to it, so know that I genuinely benefited from your post :D
