Gravitational force and electrical force

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Homework Help Overview

The discussion revolves around a hypothetical scenario where electrical attraction is considered instead of gravitational force for the Moon's orbit around the Earth. Participants are exploring the implications of substituting gravitational equations with Coulomb's law, while considering the mass of the Earth and Moon, their distance, and the forces involved.

Discussion Character

  • Mixed

Approaches and Questions Raised

  • Participants are examining the relationship between gravitational and electrical forces, questioning the validity of using gravitational equations in this context. Some are suggesting to disregard gravity entirely and focus on electric force, while others are exploring the implications of the period of the Moon's revolution.

Discussion Status

The conversation is active with various interpretations being explored. Some participants are questioning the original poster's approach and the assumptions made in their calculations. Hints and clues are being provided, but there is no explicit consensus on the best method to proceed.

Contextual Notes

There is a mention of avoiding the use of Newton's laws and focusing solely on Coulomb's law, which introduces a constraint on the approach. Participants are also discussing the implications of the formula used and its dependence on the distance variable.

leolaw
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Suppose that electrical attraction, rather than gravity, were responsible for holding the MOon in orbit around the Earth. If equal and opposite charges Q were placed on the Earth and the Moon, what should be the value of Q to maintain the present orbit? Given these data: Moon = [tex]7.35 \ast 10^{22} kg[/tex], Earth = [tex]5.98 \ast 10^{24} kg[/tex] , radius of orbit = [tex]3.84 \ast 10^8 m[/tex].

This is how I approach the problem:
I set
[tex]G \frac{m_{1}m_{2}}{r^2} = k \frac{Q^2}{r^2}[/tex]
and then solve for Q

Am I doing the right thing?
 
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Nope,u should totally disregard gravity.Wiped out.Substituted with electric force...

HINT:What is the period of Moon's revolution around Earth ??

Daniel.
 
Hmmm, I don't see anything wrong with your method leolaw. :confused:
 
Think at this way:there's suddenly no gravity and no Newton's law,just Coulomb's one...

Another clue:do you see somthing rather suspicious about his formula??

Daniel.
 
dextercioby said:
Nope,u should totally disregard gravity.Wiped out.Substituted with electric force...

HINT:What is the period of Moon's revolution around Earth ??

Daniel.
Why do you need to know the period? I should use kepler's law?
 
Not that version built with Newton's law... :wink: You can build a new one,just for the fun of it.However,you won't need the new one exactly to solve your problem...

Just apply the second law of dynamics...

Daniel.
 
dextercioby said:
Not that version built with Newton's law... :wink: You can build a new one,just for the fun of it.However,you won't need the new one exactly to solve your problem...

Just apply the second law of dynamics...

Daniel.

Second law of dynamics mean Netwon Second law? But i thought you said I should forget about Newton's law before
 
Sorry,i mislead you... :blushing: I was referring to the Law of Gravity (of Universal Attraction).

So what's the answer & how did you get it...?

Daniel.
 
phew, that's a relief. I was just about to check myself into a mental institution! :smile:
 
  • #10
dextercioby said:
Sorry,i mislead you... :blushing: I was referring to the Law of Gravity (of Universal Attraction).

So what's the answer & how did you get it...?

Daniel.
hahaa, this problem is even number on my textbook, so i don't have the answer.
But i do think that i need another way to approach this problem because i should aviod the use of law of gravity.

And by the way, why did you say there is smoething wrong with my equation before:
dextercioby said:
Think at this way:there's suddenly no gravity and no Newton's law,just Coulomb's one...

Another clue:do you see somthing rather suspicious about his formula??

Daniel.
 
  • #11
I didn't say "wrong",i said "suspicious"... :wink: Well,by your formula,the "r" wouldn't really matter,because it would simplify,right...??

Daniel.
 
  • #12
Yes, but now i have to make sure if my idea is right
 
  • #13
What idea??Don't keep it a secret... :-p

Daniel.
 
  • #14
if [tex]G \frac{m_{1}m_{2}}{r^2} = k \frac{Q^2}{r^2}[/tex] will get me the answer !
 
  • #15
Incidentally,yes...It will,though i initially advised to disregard Newton's gravity law and use the centripetal form of acceleration.

Anyway,i guess you got it solved...One way or another... :smile:

Daniel.
 

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