Roller coaster and Potential Energy

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Homework Help Overview

The discussion revolves around a physics problem involving a roller coaster and gravitational potential energy. The original poster presents a scenario where a roller coaster train moves from a height at point A to a lower point B, with specific measurements and angles provided. The task is to calculate the potential energy at both points and the change in potential energy during the descent.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the calculation of potential energy, questioning the original poster's height conversion and unit usage. There are attempts to clarify the correct interpretation of the problem's parameters, particularly regarding the angle and distance involved in the roller coaster's movement.

Discussion Status

The conversation is ongoing, with participants providing feedback on unit conversions and interpretations of the problem setup. Some guidance has been offered regarding the importance of correctly identifying the height and the implications of the angle in the calculations. Multiple interpretations of the problem are being explored, particularly concerning the height and distance measurements.

Contextual Notes

There is a noted confusion regarding the conversion of feet to meters and the interpretation of the angle's relevance to the height calculation. The original poster's calculations have been questioned, and there is a focus on ensuring accurate unit representation in the answers.

scurry18
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Homework Statement


A 1000 kg roller coaser train is intially at the top of a rise, at point A. It then moves 135 ft, at an angle of 40 degrees below the horizontal, to a lower point B.
Choose the train at point B to be the zero configuration for gravitational potential energy. Find the potential energy of the roller coaster-Earth system at points A and B, and the change in potential energy as the coaster moves.


Homework Equations


Ug=mgy


The Attempt at a Solution


Y at Point A=86.8 m
Ug= 850640 Kj

This isn't the right answer, so where am I going wrong?
 
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Check your units. Kj = 1000 Joules.
 
That still does not give me the right answer even if I divide by 1000.
 
Actually, if you'll allow me to nitpick a bit:
The unit is Joules (J), the prefix k(ilo) is written in lower case; therefore kilojoule is abbreviated kJ instead of Kj.
 
My bad! Either way, I don't get the right answer though :)
 
scurry18 said:
My bad! Either way, I don't get the right answer though :)
When you input your answer, do you also input your units? (No need to divide by 1000. The kJ was a mistake on your part.)

The problem asked for three answers. Did you input them all?
 
135 ft is not 86 m. More like 45m. Try to convert properly.
Good Luck
 
nasu said:
135 ft is not 86 m. More like 45m. Try to convert properly.
He wasn't converting, he was finding the vertical component. (He should have converted first.)

Good catch though: The distance was given in feet, not meters. D'oh! :rolleyes:
 
A, sorry. 86 is 135*Sin(40). I did not think about this.

Then this is the mistake (besides the units).
You don't need to do this (find component). 135 ft is the height, if I read the problem right. The angle doesn't matter.
 
  • #10
nasu said:
You don't need to do this (find component). 135 ft is the height, if I read the problem right. The angle doesn't matter.
That's not the way I read it.
scurry18 said:
It then moves 135 ft, at an angle of 40 degrees below the horizontal, to a lower point B.
That sounds like it moved 135 ft at an angle of 40 degrees below the horizontal.

We'll find out soon enough when the OP corrects the feet vs. meters error. :wink:
 
  • #11
Doc Al said:
That's not the way I read it.

That sounds like it moved 135 ft at an angle of 40 degrees below the horizontal.

We'll find out soon enough when the OP corrects the feet vs. meters error. :wink:

Yes, you are right. I did not focus enough...
 

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