Electric fields and equipotentials

[dasblack]

Homework Statement

The figure below shows a test charge q between the two positive charges. Find the force (in Newtons) on the test charge for q = -4 µC.
a)Give a positive answer if the force is to the right and a negative answer if the force is to the left.

b.)For the previous question, find the electric field (in Newtons/coulomb) at the position of test charge. Again, supply a positive value if the electric field points to the right and a negative value if it points to the left.

Homework Equations

F=ke|q1|q2|/r^2
E=F/qo

The Attempt at a Solution

a)F21=ke(2x10-6)(4x10-6)/(3x10-2)^2 = 80 to the left
F23=ke(4x10-6)(3x10-6)/(2x10-2)^2 = 269.7 to the right
F2 = 190

b)E=190/-4x10-6 = -4.75e7

Homework Statement

How much work (in joules) is done in moving a charge of 2.5μC a distance of 22 cm along an equipotential at 9~V?

Homework Equations

W=-change in PE, where PE = q(change in volts)

The Attempt at a Solution

W=-2.5e-6(9)= -2.25e-5 J

 

[dasblack]

Hmm I'm not sure about the negative for qo