When to Add/Subtract Kinetic & Potential Energy?

In summary, the conversation discusses using the formula KE2=KE1 + PE to solve for speed in a skiing scenario. The formula is based on the concept of conservation of energy and the assumption that the skier has zero potential energy at the bottom of the icy patch. The conversation also emphasizes the importance of understanding the concept of constant mechanical energy and the relationship between potential and kinetic energy.
  • #1
rkslperez04
31
0
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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  • #2
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.
 
  • #3
still lost...

When does it matter about the ZERO potential engery?
 
  • #4
Did you read the page I linked to?
 
  • #5
DUhhh... sure didnt.. I thought that was an underline.. BRB :)
 
  • #6
ALWAYS START OUT WITH CONSTANT MECHANICAL ENERGY.
On a given side, you will have the potential&kinetic energy for the same instant summed together.
 
  • #7
ahhhh... its amazing what happens with the light bulb comes on!
 

FAQ: When to Add/Subtract Kinetic & Potential Energy?

When should kinetic energy be added or subtracted?

Kinetic energy should be added when an object is speeding up or moving faster, and it should be subtracted when an object is slowing down or moving slower.

How do you know when to use potential energy instead of kinetic energy?

Potential energy should be used when an object is at rest or in a stationary position, such as at the top of a hill or at the bottom of a swing. Kinetic energy should be used when an object is in motion.

Can kinetic and potential energy be added together?

Yes, kinetic and potential energy can be added together to determine the total energy of an object. This is known as the law of conservation of energy.

Is there a specific formula for determining when to add or subtract kinetic and potential energy?

Yes, the formula for calculating the change in total energy is ΔE = ΔK + ΔU, where ΔE represents the change in total energy, ΔK represents the change in kinetic energy, and ΔU represents the change in potential energy.

Are there any real-life examples that demonstrate when to add or subtract kinetic and potential energy?

Yes, a roller coaster is a good example of when to add and subtract kinetic and potential energy. As the roller coaster car moves up the first hill, potential energy is increasing while kinetic energy is decreasing. As the car then goes down the hill, potential energy is decreasing while kinetic energy is increasing.

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