Coulomb's Law involving triangle

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Homework Help Overview

The problem involves three point masses arranged in a right triangle configuration, with specific distances and charges. The scenario includes a fixed mass and two other masses, one of which is subject to kinetic friction. The goal is to determine the distance at which one mass will start to move toward another, incorporating concepts from Coulomb's law and two-dimensional motion.

Discussion Character

  • Mixed

Approaches and Questions Raised

  • Participants discuss the forces acting on the masses, including gravitational and electrostatic forces. There are attempts to relate these forces to the motion of the masses and the role of friction. Some participants suggest using conservation of energy, while others question its applicability in this context. The original poster expresses confusion about how to calculate the forces involved and the initial distance between the moving masses.

Discussion Status

There is an ongoing exploration of the relationships between forces, motion, and friction. Some participants have provided guidance on drawing free body diagrams and considering the sum of forces, while others are clarifying the conditions under which the masses will begin to move. Multiple interpretations of the problem are being discussed, particularly regarding the timing of the movements of the masses.

Contextual Notes

Participants note the complexity introduced by the unknown initial distance between the moving masses and the frictional forces that may affect the motion. There is a recognition that the problem requires careful consideration of the forces at play and their interactions.

Benny851
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Homework Statement



There are three point masses. 1 is fixed in space with the 2nd point mass directly below it on the ground. The 3rd point mass is an unknown distance to the right of mass number 2. These 3 point masses for a rt triangle with point 2 at the 90 degree angle. The vertical distance between point mass 1 and 2 is 1.5 m. The mass of each point mass is 5.5kg. Also there is kinetic friction between point mass 2 and the ground. All three point masses have a charge of +15 Coulombs. If mass 3 starts moving toward mass 2, how far away from 2 will 3 be when 2 starts to move?


Homework Equations



F=MA
F=Eq
F=Qq/r^2
F=KQ/R^2

This problem seems to combine coulomb's law with with 2-d motion. However, I am stumped as to how to combine the 2 concepts. also, not knowing the original starting distance between 3 and 2 is complicating matters.

The Attempt at a Solution



I am able to calculate the force that 1 exerts on 2 no problem but have no idea how to figure out the force that 3 exerts on 2. i also have no idea how to incorporate friction
 
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It is the same as normal only now you know the origins of the forces.
Draw a free body diagram for mass 2.
 
I see what you mean. So the force acting on 2 is equal to the frictional coefficient*(mg + force of 1 acting on 2), right.

I'm thinking I use the conservation of energy equation to determine how far 3 is from 2 when 2 starts to move, is that right?
 
How does conservation of energy help here?
Why not just add up all the forces - you know what they have to sum to?
Keep the variables (it helps that all the masses and charges are the same) and solve for the distance to charge 3.
 
I am a little confused still. I have calculated the original distance between 2 and 3 before 3 starts to move from the right. Does 2 start to move at same time 3 starts to move, if so then the original starting distance is the distance from 2 that I am solving for.
 
Last edited:
Does 2 start to move at same time 3 starts to move
Of course not :)
3 starts out so far away that the friction is enough to hold 2 where it is.
As 3 approaches 2, the coulomb force increases - at some point the force will be so large that the friction no longer holds 2 in place.

All the problem wants to know is how close 3 can get to 2 without 2 moving.
 

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