# Force between two charged particles

1. Nov 19, 2013

### hk4491

1. The problem statement, all variables and given/known data

Two particles with a similar charge are held at a distance of 3.2*10^-3 m and then released. The acceleration of the first particle is measured at 7.0 m/s^2, and for the second at 9.0 m?s^2. The mass of the first particle is 6.3*10^-7. What is the mass of the second particle?

2. Relevant equations

F=ma F=G*m1*m2/r^2

3. The attempt at a solution

F1=m1a1 F2=m2a2 (where F1 and F2 are the forces exerted by each particle respectively)

F1 - F2 = G*m1*m2/r^2

(since the particles are similarly charged, they would have forces pointing in opposite directions)

after substitution and making m2 the subject of the formula:

m2 = (m1*a1*r^2)/(Gm1 + a2r^2)

which gives: m2 = 4.31*10^-7

I am not so sure if the method I used is completely correct, can someone please tell me?

2. Nov 19, 2013

### Staff: Mentor

The particles are charged. Do you really think that they will primarily feel a gravitational attraction? And to you really need to calculate the value of the force, or isn't there one of Newton's law you can use?

3. Nov 20, 2013

### hk4491

Hi, thanks for replying. Are the forces produced by the two particles equal? Because then I can use Newton's second law as such:

m1a1=m2a2

Would this be correct?

4. Nov 20, 2013

### Staff: Mentor

Yes, this is waht I was hinting at. If particle 1 feels a force from particle 2, then particle two must feel an equal and opposite force from particle 1.

5. Nov 20, 2013

### hk4491

In the second part they're asking me to find the charge of each particle. I know I should use this formula:

F = k.q^2/r^2

and solve for q. As my force should I substitute 2*ma, since there are two particles, or is one enough?

6. Nov 20, 2013

### Staff: Mentor

In essence, there are not two forces, but one that affects two particles, albeit in different directions. So no factor of two.