Unraveling Magnetism: Solving Three Common Problems

[Kadomony]

Answered

Finished! Thanks to all that helped out.

 

[stunner5000pt]

first one $$q_{1} + q_{2} = 9 * 10^{-6}C$$
thus $$q_{1} = -q_{2} + 9 * 10^{-6}C$$
$$F = k \frac{q_{1} q_{2}}{r^2}$$
in th thirdequation substitute a relation from the second equation to find just one charge. Once you have that charge sub back into 2 and solve for hte other charge.

Second one is correct F = ma = qE = eE thus a = eE/m nothing complicated about it

Third one (since you don't know E explicitly treat it like an unknown)
fir the electron
a = eE / m , v1 = 0, t = ?, d = 0.04m you know a kinematic equation to solve for this Find the expression for the time. You don't need a speicific numberic answer variables are inevitable here
now for the proton v1=0, a = eE/m, t = what you found, d = ?
once again you know the relation beween these variables. Sub in the t that you got and solve.
For simplicity do not evaluate the eE term in the first case just keep it like it is, it cancels out in the second part

 

[Andrew Mason]

1) Two positive charges, when combined, have a net charge of +9.00microcoulombs. When the charges are separated by 3.00 m, the force exerted on one charge by the other has a magnitude of 8.00 X 10^-3, Find the magnitude of each individual charge.

I'm pretty sure I have to use Coulomb's law, but obviously, I run into problems wherein I don't know the charge on either of my point charges, so I have to figure out some way to get one of them, don't I? So far, everything I've tried in order to get one of them results in a dead-end, or some bad number. If anyone could tell me how to figure out one of the charges, that'd be awesome.

When you work out the expression for the charge, as Stunner has shown, you get a quadratic equation. So it is a little trickier than he suggests.

For 3) use $d = \frac{1}{2}at^2$ so $t = \sqrt{2d/a} = \sqrt{2dm/f}$ where f = qE

AM

 

[Kadomony]

Many thanks. I'm glad that I seemed to be on the right track with the two I was having trouble with, there were just little things I didn't keep track of that I missed. I even had the q1=9-q2 thing, I just forgot to implement it.