Eletric force and gravitational force question

  • #1
strawberrysk8
27
0

Homework Statement



How many extra electrons would we have to place on earth and moon so the electric repulsion between these bodies cancels their gravitational attraction? Assume that the numbers of extra electrons on the earth and on the moon are in the same propotion as the radial dimensions of these bodies (6.38:1.74).

Homework Equations





The Attempt at a Solution

 

Answers and Replies

  • #2
LowlyPion
Homework Helper
3,115
6

Homework Statement


How many extra electrons would we have to place on earth and moon so the electric repulsion between these bodies cancels their gravitational attraction? Assume that the numbers of extra electrons on the earth and on the moon are in the same propotion as the radial dimensions of these bodies (6.38:1.74).

Homework Equations





The Attempt at a Solution


How would you think to address the problem? Can you think of any relevant formulas?
 
  • #3
strawberrysk8
27
0
F=kqq/r^2

F=GmM/r^2

Constants: k,G,m,M,r

what is q1 and q2?
 
  • #4
LowlyPion
Homework Helper
3,115
6
F=kqq/r^2

F=GmM/r^2

Constants: k,G,m,M,r

what is q1 and q2?

Don't forget the additional constraint from the OP that q_earth is 6.38 to q_moon's 1.74.

[tex]q__{earth} [/tex]= 6.38/1.74 * [tex]q__{moon}[/tex]

With all the parameters but charge determined then what do you suggest doing with the two equations?
 
  • #5
strawberrysk8
27
0
set them equal to each other

kqq/r^2 = GmM/r^2

kqq = GmM

k(6.38/1.74)q^2 = GmM

solve for q(moon)

then solve for q(earth)

what is the extra electons?
 
  • #6
strawberrysk8
27
0
oh!! i got it! thank you for the advice :)
 
  • #7
LowlyPion
Homework Helper
3,115
6
oh!! i got it! thank you for the advice :)

Congrats then and good luck.
 

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