Understanding the Work-Energy Theorem: Solving the Roller Coaster Problem

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Homework Help Overview

The discussion revolves around the application of the work-energy theorem in the context of a roller coaster problem, specifically analyzing the scenario where the roller coaster comes to rest at a height of 65m. Participants explore the implications of initial and final velocities, the net work done, and the distinction between different types of work in the context of energy changes.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants examine the assumptions regarding the final velocity of the roller coaster, questioning whether it is valid to assume it is zero. There is discussion about the net work done and its relation to kinetic energy changes. Some participants express uncertainty about the specific requirements of the question, particularly regarding the distinction between work done by a specific force versus net work.

Discussion Status

The discussion is active, with participants raising questions about assumptions and the clarity of the problem statement. Some guidance is offered regarding the interpretation of the work-energy theorem, and there is a recognition of the potential ambiguity in the question's requirements.

Contextual Notes

Participants note that the problem does not provide explicit details about certain parameters, leading to assumptions about initial and final conditions. There is mention of additional related questions that may provide further context to the problem.

john merrick
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Homework Statement
If it takes a force of 3943 N [parallel to the track] to pull the roller coaster up to point A, and it is pulled along 105 m of track, find the work done on the roller coaster.
Relevant Equations
E=1/2mv^2
height to point A is 65m. no friction. comes to rest at point A. total mass of the roller coaster is 650 kg.
the work-energy theorem states that the net work done on an object is equal to the change in kinetic energy of the object. kinetic energy is E=1/2mv^2. initial velocity is zero(problem doesn't say that but i think it is safe to assume). final velocity is zero. therefore the net work on the roller coaster is zero. is this correct?
 
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Is it safe to assume that the final velocity is zero? Isn't it better to calculate than to assume?
 
john merrick said:
therefore the net work on the roller coaster is zero. is this correct?
If the rollercoaster starts and ends at rest, then the total (net) work done on it (by all forces combined) is zero. So, yes.
 
PeroK said:
Is it safe to assume that the final velocity is zero? Isn't it better to calculate than to assume?
question states that roller coaster comes to rest.
 
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john merrick said:
question states that roller coaster comes to rest.
Okay, so the question setter has done all the work for you! I wonder what is the purpose of a question like this?

If I was setting the question, I would get you to calculate the required force, assuming we know the mass of the rollercoaster and the length and height of the tower. At least that question would have a purpose.
 
PeroK said:
Okay, so the question setter has done all the work for you! I wonder what is the purpose of a question like this?

If I was setting the question, I would get you to calculate the required force, assuming we know the mass of the rollercoaster and the length and height of the tower. At least that question would have a purpose.
that is what I'm thinking. but this is just one of the questions... there is another 4 or 5 questions related to this roller coaster problem. i only put up the information necessary to answer question 1.
 
john merrick said:
find the work done on the roller coaster.
There is a difference between the work done on a body by a given force and the net work done on the body by all forces.
The change in KE is the net work done.
It is not clear to me which is being asked for in this question.
 
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haruspex said:
There is a difference between the work done on a body by a given force and the net work done on the body by all forces.
The change in KE is the net work done.
It is not clear to me which is being asked for in this question.
you are right i think what they want is the work done on the roller coaster by a given force( you pulling it) i'll put both answers.
 
john merrick said:
you are right i think what they want is the work done on the roller coaster by a given force( you pulling it) i'll put both answers.
It seems to me that the error of this problem is to use the given relevant equation.
There is a force adding potential energy to the roller coaster, rather than a force slowing it down to a stop in its way up to point A.
 

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