Need help finishing Physics Problem, almost have answer.?

  • #1
Two Q = +5.85 mC charges are placed at opposite corners of a square d = 1.2 m on each side, and -Q = -5.85 mC charges are placed at the remaining corners, as shown in the figure.

I labeled the square A, B, C, D from top left to bottem left.

Fba = k • QA • QB / dBA2
Fca = k • QA • QC / dCA2
Fda = k • QA • QD / dDA2

Fba= -.21365
Fca= .10683
Fda= -.21365

I used the pythagorean therum to find Fba+Fda, and got .302, and then i subracted .10683 from that, but that was not the correct answer.

Any suggestions?
 

Answers and Replies

  • #2
Doc Al
Mentor
45,010
1,286
What are you asked to find?
 
  • #3
Yea, probably should have put that in,

Determine the magnitude and direction of the force on each charge.
 
  • #4
Doc Al
Mentor
45,010
1,286
Fba= -.21365
Fca= .10683
Fda= -.21365
What units are these in?
 
  • #5
They should be in Newtons
 
  • #6
Doc Al
Mentor
45,010
1,286
Redo the calculations. (You are off by orders of magnitude.)
 
  • #7
Fba = k • QA • QB / dBA2
Fba = (8.99*10^9 • (5.85)*10^-6 • (-5.85)*10^-6) / 1.2^2
Fba = (-.30766) / (1.44)
Fba = -.21365

Are my numbers off, or just my sign, or both?
 
  • #8
Doc Al
Mentor
45,010
1,286
Ah... you're using mC to mean microCoulombs. (Better to use [itex]\mu C[/itex].) In that case, the numbers look OK to me.
 
  • #9
I think you might be right, it should be milli. I will try that.
 
  • #10
I got it, 195872.2698.

Thanks for your help.
 

Related Threads on Need help finishing Physics Problem, almost have answer.?

  • Last Post
Replies
3
Views
1K
  • Last Post
Replies
4
Views
16K
  • Last Post
Replies
0
Views
2K
  • Last Post
Replies
13
Views
1K
Replies
4
Views
2K
Replies
4
Views
4K
Replies
7
Views
10K
Replies
2
Views
1K
Replies
1
Views
1K
Top