Help with with finding the magnitude of a charge

[dasblack]

1. The problem statement, all variables and given/known data
The weight of a 1.0 kg object of charge Q is just balanced by another object of equal but opposite charge fixed to a support 74 cm above it. What is the magnitude of the charge Q (in μC)?


2. Relevant equations
F=ke|q1||q2| / r^2
F=ma


3. The attempt at a solution
F=(1kg)(9.8m/s^2) = 9.8

9.8=8.99e9(q^2) / .74^2 = 24.4 uC



I think that's the right way, I'm not too sure.

Thanks

[Haths]

1. The problem statement, all variables and given/known data
The weight of a 1.0 kg object of charge Q is just balanced by another object of equal but opposite charge fixed to a support 74 cm above it. What is the magnitude of the charge Q (in μC)?


2. Relevant equations
F=ke|q1||q2| / r^2
F=ma


3. The attempt at a solution
F=(1kg)(9.8m/s^2) = 9.8

9.8=8.99e9(q^2) / .74^2 = 24.4 uC


Hmmm...

Yes equating the attrative force of electromagnetism to it's weight is the right way to go about the problem

0 = (kQq / r2) - mg

mg = (kQ2 / r2)

mgr2 = (kQ2

mgr / k = Q2

sqrt{ (mgr / k) } = Q

If that is what you've done then good on you! Numerically my answer comes out at: 2.84*10-5 C

In μC , 24μC I think...

Hope this helps!
Haths

[dasblack]

Hmmm...

Yes equating the attrative force of electromagnetism to it's weight is the right way to go about the problem

0 = (kQq / r2) - mg

mg = (kQ2 / r2)

mgr2 = (kQ2

mgr / k = Q2

sqrt{ (mgr / k) } = Q

If that is what you've done then good on you! Numerically my answer comes out at: 2.84*10-5 C

In μC , 24μC I think...

Hope this helps!
Haths

Yes, 24.4 is the answer, thank you for the help.