Finding the charge on two beads?

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Homework Help Overview

The problem involves two small insulating spherical beads placed on a taut string, which is angled and allows the beads to move frictionlessly. Each bead carries an identical positive charge, and the goal is to determine the charge on the beads based on their equilibrium position and the forces acting on them.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants discuss the forces acting on the beads, including gravitational force and the repulsive force due to the charges. There is an exploration of the conditions necessary for the beads to remain at rest, including the role of normal force and net force considerations.

Discussion Status

The discussion has progressed with participants identifying relevant forces and conditions for equilibrium. Some guidance has been offered regarding the forces involved, and there is an acknowledgment of the need for a net force of zero for the beads to remain at rest.

Contextual Notes

Participants are working within the constraints of a homework assignment, which may limit the information available for solving the problem. The discussion reflects an exploration of fundamental concepts without reaching a definitive conclusion.

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Homework Statement


Two small insulating spherical bead are placed on a taut(insulating, isolated) string which has a knot at its lower end. The string is stretched at an angle of 60degress to the horizontal. The beads can move frictionlessly on the string. The beads are given identical positive charges (which are distributed evenly over the tiny volumes of the beads). The lower bead rests against the knot. The other bead comes to rest 5cm away from the knot on the string. The mass of each bead is 0.1g. What is the charge on the beads?

Homework Equations




The Attempt at a Solution


Would I use work? Or something else? Not quite sure
Just an idea of even what equation to start with would be nice
 
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Think about how it is possible that the bead can remain at rest. What forces act on the bead?
 
well there would be the force that pushes the two beads apart, and gravity?
 
TSny said:
Think about how it is possible that the bead can remain at rest. What forces act on the bead?

Well there would be the force that pushed the two beads away, and gravity?
 
janetxo said:
Well there would be the force that pushed the two beads away, and gravity?

Yes. But there is a third force. Hint: The bead is in contact with the string.

What is the condition that must be met by these 3 forces for the bead to remain at rest?
 
TSny said:
Yes. But there is a third force. Hint: The bead is in contact with the string.

What is the condition that must be met by these 3 forces for the bead to remain at rest?

So, a normal force between the bed and the string? (as there is no friction). and the net forces would have to be 0 in order for it to be at rest. Fnet=ma=0.
 
janetxo said:
So, a normal force between the bed and the string? (as there is no friction). and the net forces would have to be 0 in order for it to be at rest. Fnet=ma=0.
Yes, that's right.
 
TSny said:
Yes, that's right.

thanks for walking me through that bit! Wasnt quite sure how to start, :) really apperiate it
 
Good work. Welcome to PF!
 

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