Finding charge magnitude when weight is balanced by electrostatic force

[dasblack]

Homework Statement

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)?

Homework Equations

F=ke|q1||q2| / r^2
F=ma

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]

Homework Statement

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)?

Homework Equations

F=ke|q1||q2| / r^2
F=ma

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.