More quick work and energy questions

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Homework Help Overview

The discussion revolves around questions related to work and energy, specifically focusing on kinetic energy during collisions and the effects of air resistance on gravitational potential energy. Participants are exploring the relationships between initial and final kinetic energies in different scenarios.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants are attempting to determine the ratio of final to initial kinetic energy after an object bounces back from a wall. There is confusion regarding the calculations and the effects of speed reduction on kinetic energy. Questions are raised about how to properly express these ratios mathematically, particularly in the context of energy loss due to air resistance.

Discussion Status

There is ongoing exploration of the problem with various participants questioning their understanding of kinetic energy ratios. Some have provided guidance on how to set up the calculations, while others express uncertainty about the correct approach. Multiple interpretations of the problem are being discussed, but no consensus has been reached.

Contextual Notes

Participants are considering the effects of air resistance and the implications it has on energy calculations, which adds complexity to the problem. There is also a focus on ensuring the correct application of kinetic energy formulas in the context of the given scenarios.

future_vet
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An object hits a wall and bounces back with half if its original speed. What is the ratio of the final kinetic energy to the initial kinetic energy?
I am not sure I understand the question, is it 1:2?

A ball drops some distance and gains 30 J of kinetic energy. Do not ignore air resistance. How much gravitational potential did the ball lose?
I would say more than 30J since we have to take air resistance into consideration.

Thanks!
 
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future_vet said:
An object hits a wall and bounces back with half if its original speed. What is the ratio of the final kinetic energy to the initial kinetic energy?
I am not sure I understand the question, is it 1:2?

Not so fast. Write down the kinetic energies and look at the ratio.
 
First is 1 and second is 0.5 => 1/0.5 =2. Is this correct?
 
future_vet said:
First is 1 and second is 0.5 => 1/0.5 =2. Is this correct?

No, it isn't. The first kinetic energy is 1/2 m v^2, and the second is 1/2 m (1/2 v)^2. What is their ratio?
 
future_vet said:
First is 1 and second is 0.5 => 1/0.5 =2. Is this correct?

No - the kinetic energy of the object is (1/2)mv^2.
 
I am not sure I get it, but it looks like 1:0.5 to me...
 
future_vet said:
I am not sure I get it, but it looks like 1:0.5 to me...


Do you know how to take the ratio of 1/2 m (1/2 v)^2 (final kinetic energy) and 1/2 m v^2 (initial kinetic energy)?
 
I guess not... It's ok, I'll figure it out.

Thanks!
 

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