How do we find the equivalent voltage in a parallel circuit?

[hsnelect]

Homework Statement

[PLAIN]http://img600.imageshack.us/img600/7497/prob2.jpg

Homework Equations

I = V / R

The Attempt at a Solution

I tried to add the 3 voltages together but i didn't get a correct answer ..
I guess I'm missing something that has to be with the parallel Circuit or something like that ..
so how do we get the equivalent voltage ??

Thanks!

 

[tiny-tim]

welcome to pf!

hi hsnelect! welcome to pf!

you need to apply Kirchhoff's rules …

call the currents I₂ I₄ and I₅ …

what do you get? ​

 

[willem2]

Assign a potential of 0 to the bottom right of the circuit.
Assign a Potential of V to the point where V1 and the 4 and 5 ohm resistances mee

work out the currents through the 3 branches of the circuit.
for example the potential across the 5 ohm resistance is V - V3 so the current through it is $(V - V_3)/ 5$

Now you can apply Kirchhof's current law, and then solve for V. The currents can
then be found with the 3 equations you found worked out above.

I don't think that adding the 3 voltages is going to get you anywhere. It seems you
might mean the the superposition principle: If you calculate the currents with only V1 in the circuit and the other voltage sources replaces by a wire, and calculate the currents through the resistances, and then you repeat this with V2 and V3, you can then sum the 3 currents you found for each resistance to get the current through that resistance with all the voltage sources present. I don't think that's an efficient method here.