AP physics C E and M

Question

A point charge of +18 μC is on the y axis at y = +3.00 m.

 

A point charge of -12 μC is at the origin.

 

A point charge of +45 μC is on the x axis at x = +3.00 m. 

1. Determine the magnitude of the net electrostatic force, in Newtons, acting on the charge at x = +3.00 m.
2. Find the angle, in degrees, of the force relative to the negative x-axis.

Answer 1

 pay attention to triangle, it is isosceles one, that is, angles of 45⁰

F_{net, x}=k(q₁ q₂)cos(45)/18 -k(q₁q₂)/9

F_{net, y}= k(q₁ q₂)sin(45)/18

 F_net=[(F_{net, x})² +(F_{net, y})²]^1/2

And tanθ= F_{net, y}/ F_{net, x} , then θ=tan^-1(F_{net, y}/ F_net)