How Do You Calculate the Electric Charge on a Suspended Cork Ball?

[astroman707]

Homework Statement

A cork ball is suspended at an angle from the vertical of a fixed cork ball below. The mass of the suspended ball is 1.5x10^-4 kg. The length of the suspension thread is .1m. The fixed ball is located .1m directly below the point of suspension of the suspended ball. Assume that when equal electric charges are placed on the two balls, the electric repulsive force pushes the suspended ball up so it's thread makes an angle of 45 degrees with the vertical. What is the magnitude of the electric charge?

Homework Equations

f= k (q x q)/ r^2
T=IA

The Attempt at a Solution

I drew a line from the fixed ball to the suspended ball, and using the (.1)sin(45degrees), I got R= .071.
I then calculated the weight force of the suspended ball, which is .00147N.
I thought I could used a torque formula to solve for the force, but it wasn't working. So I tried breaking up the weight force and the coulomb force into vector components and making those components equal to each other and solving for q, but the x and y components had different values for q, which doesn't make sense.

 

[BvU]

the x and y components had different values for q

how so ? Can you post a drawing of what you did ?

 

[ehild]

Homework Statement

A cork ball is suspended at an angle from the vertical of a fixed cork ball below. The mass of the suspended ball is 1.5x10^-4 kg. The length of the suspension thread is .1m. The fixed ball is located .1m directly below the point of suspension of the suspended ball. Assume that when equal electric charges are placed on the two balls, the electric repulsive force pushes the suspended ball up so it's thread makes an angle of 45 degrees with the vertical. What is the magnitude of the electric charge?

Homework Equations

f= k (q x q)/ r^2
T=IA

The Attempt at a Solution

I drew a line from the fixed ball to the suspended ball, and using the (.1)sin(45degrees), I got R= .071.
I then calculated the weight force of the suspended ball, which is .00147N.

What is R?How is it related to the problem?

I thought I could used a torque formula to solve for the force, but it wasn't working. So I tried breaking up the weight force and the coulomb force into vector components and making those components equal to each other and solving for q, but the x and y components had different values for q, which doesn't make sense.

what are the directions of the coordinate axes x and y?
How many forces act on the suspended cork? It looks that you forgot the tension force.