Find the Force and Direction of a charge

[topM]

Homework Statement

http://www.brainmass.com/homework-help/physics/electromagnetic-theory/98519
That site has the diagram of the Lab and distances.

R_g-r=sqrt 3.709² + .533² = 3.75
F_g-r= K(q₁)(q₂)/R_g-r²= (8.99x10⁹)(1x10^-5)(1x10^-5)/3.75² = .064
angle 1 = tan^-1(.533/3.709) = 8.18 degrees

R_b-r=sqrt 2.553² + 2.709² = 3.72
F_b-r= K(q₁)(q₂)/R_g-r²= (8.99x10⁹)(1x10^-5)(1x10^-5)/3.72² = .065
angle 1 = tan^-1(2.533/2.709) = 43 degrees

Fx_g-r = (.064)Cosine8.18 = .063
Fy_g-r = (.064Sine8.18 = .009

Fx_b-r = (.065)Cosine43 = .048
Fy_b-r = (.065)Sine43 = .044

Fx = .063 + .048 = .111
Fy = .009 + .044 = .053

Force = sqrt of .111² + .053² = .123N
Angle = tan^-1(.64/.65) = 45 degrees + 8.18 = 53 degrees to the + X

The lab shows that the total Force = .185N
Where did I go wrong??

 

[diazona]

It's kind of hard to tell, but it looks like you calculated the force on the charge at t = 0, that is, as soon as it is released. The problem is asking for the force after 1 second. To figure it out you'd have to write and solve a differential equation for the charge's position as a function of time... seems like a rather unpleasant thing to have to do :-( Are you sure you're supposed to calculate this?