Kinetic Energy of Charged Particle

[soccerj17]

[SOLVED] Kinetic Energy of Charged Particle

Homework Statement

Particles A (of mass m and charge Q) and B (of m and charge 5Q) are released from rest with the distance between them equal to 0.9976 m. If Q=33e-6 C, what is the kinetic energy of particle B at the instant when the particles are 2.9976 m apart?

Homework Equations

U=kq1q2/r
K=(mv^2)/2
ΔU+ΔK=0
F=ma

The Attempt at a Solution

I solved for the potential energy at both distances using U=kq1q2/r to find Ui=49.0683 J and Uf=16.3299 J. Then I used conservation of energy to find K so K=Ui-Uf and got K to be 32.7384 J. But I'm not sure how to get just the kinetic energy of particle B. I tried to sum the forces and use Newton's third law to find acceleration to see if that would help but I don't know how to find it without knowing the mass. I'm not sure if maybe I have to do a ratio to find the energy? I don't know what to do.

 

[soccerj17]

nevermind, i figured out its just half of the system kinetic energy

 

[Moetasim]

The kinetic energy of particle B can be found by using the equation K=(mv^2)/2, where m is the mass of particle B and v is its velocity. We can use the given information about the charges and distances to find the force acting on particle B due to particle A, and then use F=ma to find the acceleration of particle B. The mass of particle B can be found using the given information about its charge and the charge-to-mass ratio of an electron. Once the mass and acceleration of particle B are known, its kinetic energy can be calculated using the above equation.