What Is the Mass of the Second Particle and the Magnitude of the Charges?

[Saladsamurai]

Homework Statement

Two equally charged particles are held 3.2*10^(-3)m apart and released from rest. The initial acceleration of the first is 7 m/s^2 and that of the second is 9 m/s^2.

If the mass of the first is m1= 6.3*10^(-7) kg, what are a) the mass of the second particle and b) the magnitude of the charge of each?

Homework Equations

F=ma
F=kq1q2/r^2

The Attempt at a Solution

I just need a kick in the right direction here. I am looking at a worked solution to the first part and they make the assumption

F1=F2 , thus, m1a1=m2a2

But, for some reason I am uneasy with this. Why are these two forces equal?

Sorry for the lame question... I am out of practice and am trying to do some review.

Thanks

 

[nrqed]

Homework Statement

Two equally charged particles are held 3.2*10^(-3)m apart and released from rest. The initial acceleration of the first is 7 m/s^2 and that of the second is 9 m/s^2.

If the mass of the first is m1= 6.3*10^(-7) kg, what are a) the mass of the second particle and b) the magnitude of the charge of each?

Homework Equations

F=ma
F=kq1q2/r^2

The Attempt at a Solution

I just need a kick in the right direction here. I am looking at a worked solution to the first part and they make the assumption

F1=F2 , thus, m1a1=m2a2

But, for some reason I am uneasy with this. Why are these two forces equal?

Sorry for the lame question... I am out of practice and am trying to do some review.

Thanks

They form an action-reaction pair (Newton's third law). They must be equal!

 

[nicksauce]

F = q1q2 /r^2

q1q2 is the same for both particles, as is r.

 

[Saladsamurai]

They form an action-reaction pair (Newton's third law). They must be equal!

I guess I can live with that.