When to Add/Subtract Kinetic & Potential Energy?

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Homework Help Overview

The discussion revolves around understanding the principles of kinetic and potential energy in the context of a skier moving downhill. The original poster questions when to add or subtract these forms of energy, particularly in relation to a specific problem involving a skier's speed on an icy patch.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants explore the conservation of mechanical energy and the conditions under which kinetic and potential energy are combined. Questions arise about the significance of the reference point for potential energy and how it affects calculations.

Discussion Status

Some participants have provided insights into the conservation of energy principle, suggesting that the total mechanical energy remains constant in the absence of friction. However, there is still some confusion regarding the reference point for potential energy and its implications for the problem.

Contextual Notes

There is a mention of a specific formula related to kinetic and potential energy, and participants are discussing the implications of choosing a reference point for potential energy. The original poster expresses uncertainty about the application of these concepts in the given scenario.

rkslperez04
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Im wondering how do we know when to substract Kinetic engery from potential engery or when do we add them?

Is that making sense?


question is asking:
a women skis downhill at a constant speed of 8.0 m/s when she reaches an icy patch on which her skis move with negligible friction. If the icy patch is 10 m high, what is the skier's speed at its bottom?

the book says to use this formula:
KE2=KE1 + PE


why are adding kinetic and potential together? I understand how to manipulate the equaiton to solve for speed but why are we using this formula?
 
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The sum forms the total (mechanical) energy. In the absense of friction, it's a contant (conservation of energy). Since it doesn't matter where the "zero" of potential energy is, assume the skier has P.E = 0 at the bottom of the icy patch.
 
still lost...

When does it matter about the ZERO potential engery?
 
Did you read the page I linked to?
 
DUhhh... sure didnt.. I thought that was an underline.. BRB :)
 
ALWAYS START OUT WITH CONSTANT MECHANICAL ENERGY.
On a given side, you will have the potential&kinetic energy for the same instant summed together.
 
ahhhh... its amazing what happens with the light bulb comes on!
 

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