Question

A point charge Q = -400 nC and two unknown point charges, q1 and q2, are placed as shown. Point charge q1 is located 1.3 meters along the +x-axis, point charge q2 is located 0.7 meters down the -y-axis, and point charge Q is located 2.0 meters from the origin at an angle of 30° above the x-axis. At the origin, the three charges together create an electric field that has magnitude zero. What is the charge q2?


A) -25nC

B)100nC

Answer 1

Looking just at location and charges:
draw a sketch.
For Q, the E is pointed up the 30 degee vector to the NE
to counter that, q1 and q2 have to be opposite direction in E at origin, so on q2 component, it has to be negative to make the E field down below the x axis, and q1 has to be + to make E point to the left.
Q1 is +, Q2 is -. Only A is a negative charge.

Answer 2

100nC