What Is the Initial Separation Between Two Charged Particles?

AI Thread Summary
The discussion focuses on calculating the initial separation between two charged particles with equal charges and different masses after they are released. The user initially attempted to use energy conservation principles but realized that both particles should be included in the kinetic energy calculations. They propose using the conservation of momentum to find the velocity of the second particle, as the net force on the system is zero. However, this introduces two unknowns: the velocity of the second particle and the initial distance between the particles. The conversation emphasizes the need to correctly account for both particles in the energy and momentum equations to solve for the desired variables.
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One particle has a mass of 3.00x10^-3 kg and a charge of +7.80 µC. A second particle has a mass of 6.00x10^-3 kg and the same charge. The two particles are initially held in place and then released. The particles fly apart, and when the separation between them is 0.100 m, the speed of the 3.00x10^-3 kg particle is 130 m/s. Find the initial separation between the particles.

Using the information given from the 3x10^-3 kg particle, I tried to use enegry to solve the problem. EPEinitial=EPEfinal+KE I subsituted and eventually ended up with kq^2/r(initial)=kq^2/r(final)+1/2mv^2. I solved the equation for r(final) and I got an answer that made sense, but it was not the right answer. Can anyone tell me what I am doing wrong?
 
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remember that with energy problems you have to keep in mind what the "system" is that you are evaluating. In this case, the system contains BOTH particles, so the right side of the equation should contain two kinetic energy components (one for each particle).
The new question now is what is the speed of the other particle?
 
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If you take the system as a whole, net force is zero. So may be we can use the conservation of mometum to find the velocity of the other particle
 
So if I add the other kenetic energy to the other side of the equation I get kq^2/r(initial)=kq^2/r(final)+1/2mV^2+1/2mv^2. Instead of one unknown in the equation I now have two, the velocity of the second particle and the initial distance between the particles? How do I go about getting the velocity of the second particle?
 
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