Question regarding Coulomb's Law

[Keshav Santhanam]

Homework Statement

Three separate spheres next to each other. The one on the left is positive (charge of +25.5μ C). The one on the right is negative(-25.5μ C). The two are separated by 0.25m. The third sphere has a charge of +2.5μ C and is placed exactly halfway between the two. Find the force on the first, second, and third object(with direction, of course). (To clarify, the problem is asking for the total force on the first object (from the other two), etc.)

Homework Equations

Coulomb's law

The Attempt at a Solution

I successfully found the charge between the spheres on the left and right (completely disregarding the third one in the middle). That gave me 93.6 N.

That's about it because I can't seem to visualize the movement of all three objects. Help would be appreciated!

EDIT: I have the answers, just forgot to add them in here:
73.14 N is the force on the middle object (rightward)
The leftmost sphere: 56.92 N right
The rightmost sphere: 36.7 N right

 

[gneill]

I successfully found the charge between the spheres on the left and right (completely disregarding the third one in the middle). That gave me 93.6 N.

Can you show us how you did that? I'm curious because there's no mention in the problem statement of the distances between the spheres

 

[Keshav Santhanam]

Can you show us how you did that? I'm curious because there's no mention in the problem statement of the distances between the spheres

Well, I had to screw something up on my first post
I will add it in now.

 

[gneill]

Okay, so have you drawn a sketch of the layout and penciled in the distances between the centers of all the spheres?

That's about it because I can't seem to visualize the movement of all three objects. Help would be appreciated!

I think you need to assume that all the spheres are fixed in place, so that there's no movement involved.

 

[Keshav Santhanam]

Okay, so have you drawn a sketch of the layout and penciled in the distances between the centers of all the spheres? I think you need to assume that all the spheres are fixed in place, so that there's no movement involved.

I think I see where you are coming from. Would the sphere the force is acting upon be free to move? Or none at all? The directions didn't specify.

 

[gneill]

I think I see where you are coming from. Would the sphere the force is acting upon be free to move? Or none at all? The directions didn't specify.

Presume that they are not free to move. They are fixed in place.

 

[Keshav Santhanam]

Presume that they are not free to move. They are fixed in place.

I think if they were free to move the forces between them would continuously change (because the force is proportional to distance squared). So, them being stationary makes sense, but I recall my teacher stating that in each part of the problem a different sphere was free to move.
If we assume they are fixed, how would I set up this problem? Should I cancel the forces of either sphere (the ones on the ends) while solving for the one in the middle, etc?

 

[gneill]

So, them being stationary makes sense, but I recall my teacher stating that in each part of the problem a different sphere was free to move.

Without seeing the problem in full, I can only surmise that they will be looking for initial accelerations or something similar (assuming that the spheres have mass values).

If we assume they are fixed, how would I set up this problem? Should I cancel the forces of either sphere (the ones on the ends) while solving for the one in the middle, etc?

Yes. Forces are vectors and add as such.

 

[Keshav Santhanam]

Without seeing the problem in full, I can only surmise that they will be looking for initial accelerations or something similar (assuming that the spheres have mass values).Yes. Forces are vectors and add as such.

I think I might just have to ask my teacher about this one. That was all the information given. Thanks for the help though, I appreciate it!