• Support PF! Buy your school textbooks, materials and every day products Here!

Eletric force and gravitational force question

  • #1

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
3,090
4

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
F=kqq/r^2

F=GmM/r^2

Constants: k,G,m,M,r

what is q1 and q2?
 
  • #4
LowlyPion
Homework Helper
3,090
4
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
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
oh!! i got it! thank you for the advice :)
 
  • #7
LowlyPion
Homework Helper
3,090
4
oh!! i got it! thank you for the advice :)
Congrats then and good luck.
 

Related Threads on Eletric force and gravitational force question

Replies
2
Views
3K
  • Last Post
Replies
2
Views
853
Replies
2
Views
2K
Replies
2
Views
961
  • Last Post
Replies
0
Views
941
  • Last Post
Replies
1
Views
892
  • Last Post
Replies
5
Views
2K
Replies
1
Views
892
  • Last Post
Replies
9
Views
2K
  • Last Post
Replies
4
Views
9K
Top