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1. A charge A of -5 µC has two nearby charges: +3.0 µC at a distance 0.3 m vertically above it, and +4.0 µC at a distance of 0.4 m horizontally. Find the magnitude of the force in newton on charge A. Hint: find the vertical and horizontal components, then add these vectors to obtain the resultant.

2. Two charges of +1 and +36 nanocoulomb are separated by a distance of 100 mm. A 3rd test charge is moved along the line between these two charges. Where is the test charge when it experiences a net force = zero?

Give your answer in mm measured from the first of the two charges. Hint: think about the ratio of the two charges and deduce a ratio for the distances.

The attempt at a solution

1. Using the formula |F| = k[(|q1||q2|)/r^2)]

I found Fhorizontal = 1.12*10^-6

and Fverticle = 1.5*10^-6

I then use pythag, resultant = sqrt( (F_horizontal)^2 + (F_vertical)^2 )

to give answer of 1.87*10^-6.

I think it may be right, can somebody verify?

2. I'm not sure how to do this one!

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# Homework Help: Resultant force formula

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