Finding Kinetic Energy from graph of Power

AI Thread Summary
To find kinetic energy from a power graph, the integral of the power represents the work done, which is equal to the change in kinetic energy. While the initial approach suggests using triangular areas for estimation, the curves are not strictly triangular, indicating a need for a more accurate representation, possibly through nonlinear equations. The Work Energy Theorem states that net work equals the change in total energy and kinetic energy, raising the question of whether potential energy factors into the problem. The vagueness of the question complicates the estimation process, as it does not specify the accuracy required. Ultimately, approximating the curves as sine or negative quadratic may provide a more reliable estimate for kinetic energy.
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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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