Potential + Kinetic Energy Question

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Homework Help Overview

The discussion revolves around a physics problem involving kinetic and potential energy of a model plane during a dive. The original poster presents calculations for kinetic energy and potential energy changes, expressing confusion regarding the energy lost during the dive and the energy gained in kinetic form.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants explore the relationship between potential and kinetic energy, questioning how energy is conserved during the plane's dive. Some discuss the implications of energy loss versus energy conversion, while others clarify the conservation of energy principle.

Discussion Status

Participants are actively engaging with the problem, offering insights into energy conservation and potential energy loss. There is a recognition of the need to clarify the original poster's understanding of energy transfer during the dive, with some guidance provided on how to approach the calculations.

Contextual Notes

There is an emphasis on the conservation of energy, with participants noting that energy cannot be lost but rather transformed. The original poster's calculations and assumptions are under scrutiny, with a focus on ensuring clarity in understanding the energy dynamics involved.

NDiggity
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Homework Statement


A 15.0 kg. model plane flies horizontally at 12.5m/s. Part a) asks for kinetic energy. I got 1172J. Part b) says the plane goes into a power dive and levels off 20.4 m closer to the earth. How much energy did it lose during the dive. I got 2998.8J. Doesn't really make sense.

Then part c) asks how much kinetic energy did the plane gain during the dive. I'm lost. Please help.
 
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the first question is right.

the second one, "how much do it loose"
well since it is falling, it must loose some potential energy. But energy can not be destroyed; so it does not loose any total energy.

Think of this:
When you let a rock fall free from a buildning, an ignore air resistance, what is happening with the rock from an energy point of view?
 
It is transfering potential to kinetic. So for part b) it loses no energy. For part c) i found out the potential energy it would lose to be 2998 J. So the kinetic energy gained 2998 J. Part D asks what the new kinetic energy would be, so I added 1172 and 2998. Is this better? PS, thank you for your help. I appreciate how no matter how basic some of the question I ask are, no one is sarcastic or demeaning.
 
Last edited:
for part (b) i guess the question should have been, how much potential energy the plane has lost? then you use the equation to find the potential energy converted to kinetic energy.

using the law of conservation of energy, potential energfy lost = kinetiv energy gained.

i think you're right for part (d)
 
Energy is conserved, so NDiggity is correct. No energy is lost, the plane travels faster in the lower orbit. The drop in potential energy is offset by the gain in kinetic energy [disregarding friction].
 

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