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Coulomb's Law, find the acceleration

  • Thread starter Dougggggg
  • Start date
  • #1
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Homework Statement


Suppose the the earth were made only of protons, but had the same surface size and mass it presently has. What would be the acceleration of an electron released at the surface? Disregard gravitation force.


Homework Equations


F=(keq1q2)/r2


The Attempt at a Solution


I solved for the number of protons and got something like 3.57 X 1051

Since that would be multipled by the charge of the proton, I just squared my charges and set the above number as "n." Solved for "a." My number was something times 1073 but my friend got something times 1090

Do either of these sound correct?
 

Answers and Replies

  • #2
155
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Ok, now I have gotten times 10 to the 40th, and 10 to the 46th. Can someone at least tell me to what power of ten their answer was? I cannot seem to get a consistent answer to save my life.
 
  • #3
1,137
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How did you got two answers? please tell me.

and mine is <something> x 1040
 
  • #4
gneill
Mentor
20,793
2,773
I solved for the number of protons and got something like 3.57 X 1051

Since that would be multipled by the charge of the proton, I just squared my charges and set the above number as "n." Solved for "a." My number was something times 1073 but my friend got something times 1090

Do either of these sound correct?
I don't see "n", and I don't see "a" in any of the formulas that you've provided (only one!).

How about writing a few lines showing your intermediate results?
 
  • #5
155
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F=ma=n(Coulomb's Law equation).

Got that answer to the 40th like 2 times in a row, I'm starting to think I am just bad at typing too many things in scientific notation.

The reason I could put in that value for n was because I was multiplying it by the charge. Either way, checked with my prof, turns out the answer <something> to the 40th was right.
 
  • #6
SammyS
Staff Emeritus
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F=ma=n(Coulomb's Law equation).

Got that answer to the 40th like 2 times in a row, I'm starting to think I am just bad at typing too many things in scientific notation.

The reason I could put in that value for n was because I was multiplying it by the charge. Either way, checked with my prof, turns out the answer <something> to the 40th was right.
Do you mean,

F = m·a = n·FCoulomb, where n is the number of protons you computed, FCoulomb is the Coulomb force between two protons separated by some distance, r, and m is the mass of ___ ... ?
 
  • #7
155
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Exactly, and the mass would be the electron since that is the acceleration I am trying to find.
 
  • #8
322
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a=0 bro, how can an electron accelerate towards protons when its released from the surface?
 
  • #9
1,137
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@ Liquidxlax
Its just a way of saying that you need not to consider the height of electron and distance b/w their centres is R of earth!!
why would someone give that simple question!!!

______________

@ Dougggggg

This method is right!!
how you got the other answer?
And especially that 1073 one!!!
 
  • #10
155
0
I'm not sure, graphing calculators are not my friend, I do as many calculations as I can in my head usually before I resort to putting things in my calculator.
 

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