Finding Kinetic Energy from graph of Power

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Homework Help Overview

The discussion revolves around estimating kinetic energy from a power graph, focusing on the relationship between power, work, and kinetic energy. Participants are exploring how to interpret the area under the power curve to determine work done and its implications for kinetic energy.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants discuss the integral of the power graph as a representation of work done and its equivalence to kinetic energy. There are attempts to approximate the area under the curve using geometric shapes, while others question the appropriateness of this method given the non-linear nature of the graph. The role of potential energy in the context of the problem is also raised, along with concerns about the vagueness of the question.

Discussion Status

The discussion is ongoing, with participants offering various interpretations and approaches to the problem. Some guidance has been provided regarding the Work Energy Theorem, and there is an acknowledgment of the need for clarity in the problem statement. Multiple interpretations of the power graph are being explored, but no consensus has been reached.

Contextual Notes

Participants note the ambiguity in the problem's requirements, particularly regarding the estimation accuracy and the potential influence of potential energy on the kinetic energy calculations. The lack of specific details in the question is acknowledged as a complicating factor.

mintsnapple
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Homework Statement


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Homework Equations


P = dW/dt
Change in work = Change in Kinetic Energy


The Attempt at a Solution


Since the integral of the power graph is work done in the system, and since it starts at 0, does this mean kinetic energy is the same thing? So I can probably make a triangle with a height of 20 and base 1 to get an area of 10 for the first problem? And then 30 for the next one?

Though I feel this is much more complicated than that...
 
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mintsnapple said:
I can probably make a triangle with a height of 20 and base 1 to get an area of 10 for the first problem? And then 30 for the next one?
Yes, except that they are clearly not triangles. Can you think of a nonlinear equation that might better represent those curves?
 
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haruspex said:
Yes, except that they are clearly not triangles. Can you think of a nonlinear equation that might better represent those curves?
The question says estimate, so would an equation for the curve be necessary?

Also, one of the tutors explicitly said there were two things to the Work Energy Theorem:
1. The net work on a system is equal to the change in total energy of
that system.
2. The net work on a structureless element of a system is equal to the
change in kinetic energy of that element.

My concern: Does potential energy play any part in this problem?
 
mintsnapple said:
The question says estimate, so would an equation for the curve be necessary?

Also, one of the tutors explicitly said there were two things to the Work Energy Theorem:
1. The net work on a system is equal to the change in total energy of
that system.
2. The net work on a structureless element of a system is equal to the
change in kinetic energy of that element.

My concern: Does potential energy play any part in this problem?
The question is really much too vague. If you allow for the possibility that some of the power has gone into potential energy (e.g. pushing it against a strong electric field) then all you can hope to do is provide an upper bound on the KE.
Since it doesn't say how accurate the estimate is to be, yes, you could just treat the curve as a sawtooth, but by the same argument you could just estimate 0.
So we are left to guess what is wanted. My guess would be to approximate the curves as either sine or negative quadratic.
 
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