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Four Charges

  • Thread starter Bryon
  • Start date
  • #1
99
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Homework Statement


Four charges q1 = q3 = -q and q2 = q4 = +q, where q = 4 µC, are fixed at the corners of a square with sides a = 1.3 m.

q1 M' q4







q2 q3




(b) Find the force on a test charge Q = -0.3 µC placed at the midpoint M' of the top side of the square


Homework Equations


Coulombs law: F = (k*q1*q2)/r^2


The Attempt at a Solution


Fq1M' = (k(4uC)(0.3uC))/(0.65^2) = 0.025533728
Fq4M' = 0.025533728

theta = tan^(-1)(0.65/1.3) = 26.56505118 degrees
90-26.56505118 = 63.43494882 degrees

Fq2M'x = -0.025533728(cos(63.43494882)) = -0.01141903
Fq3M'x = -0.01141903

FM',net = 2(-0.01141903) + 2(0.025533728) = 0.028229396N

Which is wrong of course. Where did I mess this up at?
 

Answers and Replies

  • #2
Delphi51
Homework Helper
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Fq2M'x = -0.025533728(cos(63.43494882))
You can't use the .0255 again because q2 and Q are not .65 m apart.
 
  • #3
99
0
oh yeah....that was a really silly mistake on my part. Thanks!
 
  • #4
Delphi51
Homework Helper
3,407
10
Most welcome, Bryon.
 

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