Particle Kinetic energy problem

AI Thread Summary
The discussion centers on calculating the kinetic energy of particle B when two charged particles are released from rest and move apart due to their repulsive Coulombic force. The user expresses confusion about applying conservation of energy and determining the final kinetic energy without knowing particle A's velocity. Suggestions include identifying the forces acting on the particles, applying Newton's second law, and solving for their velocities over time. The importance of focusing on the Coulombic force while neglecting gravity is emphasized. The user remains uncertain about the direction of the forces and the correct setup for the equations.
Punchlinegirl
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Particles A (of mass m and charge Q) and B (of mass m and charge 5Q) are released from rest with the distance between them equal to 0.9773 m. If Q = 8 \mu C, what is the kinetic energy of particle B at the instant when the particles are 2.9773 m apart? Answer in units of J.
I really don't know how to do this problem. I tried to set it up by using conservation of energy.
KE_A + KE_B + U_A + U_B = KE_A + KE_B + U_A + U_B
qkQ/.9773 + qk5Q/.9773 = KE_A + KE_B + qkQ/2.9773 + qk5Q/2.9773.
I really don't think this setup is right, and I have no idea how I would be able to solve for the final kinetic energy of B when I don't know the final velocity of A.
Suggestions?
 
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1)Start out with determining what force is acting between those particles. Also, make sure that you have the correct direction of the force vector with respect to an X and Y axis.

2)Apply Newton's second Law in both the X and Y direction.

3) Solve the equations to get the particles' velocity and positions as a function of time

marlon
 
Since the particles both have a positive charge, I know they will repel. Aside from that force, the normal force and gravity, those are the only forces I know of. Is that right?
 
Coulombic force and gravity, yes.

Though in this problem, i think you can omit gravity.

marlon
 
Wouldn't the columbic force just be in the x-dir? So it would be like
qE_b- qE_a= ma ?
Sorry... I'm still confused.
 

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