Jumping a dead battery in a car

[Eastonc2]

Homework Statement

so the problem, along with the figure, can be found http://www.cramster.com/answers-nov-09/physics/problem-3268-12-car-battery-dies-somuch-volt_697332.aspx?rec=0

Homework Equations

I=V/R,

The Attempt at a Solution

I am able to calculate parts a and b, however, once the batteries are in parallel, I am completely confounded. The concept of the current that would be running through the dead battery completely eludes me.

 

[SammyS]

Have you learned to use Kirchhoff's Laws?

That should do it.

 

[Eastonc2]

Ok, so, how do I take the second, 'dead', battery into account? I am actually working on a slightly different problem in terms of voltage and resistance, but the arrangement is essentially identical. Do I calculate the current that it would pass through the resistors as well? it's just that when we went over kirchhoffs laws we didn't really cover any instances involving batteries in parallel like this, and it's really throwing me for a loop lol, get it? sorry bout that last part...

 

[Eastonc2]

What I'm trying to find is a break down of the work required. I know how to do the calculations, I am just unsure of how the numbers would work out because of this second battery. I might be approaching this thinking it's more complicated than it actually is, but I see that second battery, the dead one, and don't know what to do with it, and the effect it has on the rest of the circuit.

 

[SammyS]

You will need voltage equations for two of the three possible loops.

You may need a junction equation, depending upon how you define the currents.

 

[Eastonc2]

so, I guess what I'm looking for is, can the dead battery still pass current through the right loop given that the battery on the left is charging it?

 

[netgypsy]

Set up your Kirchoff equations for the loops and your currents in and out of a junction. Just make a guess as to the direction of the current through the second battery if you have no intuition about it. Solve and if you chose the wrong direction you'll get the opposite sign. Once you solve for the currents it should make sense to you.

 

[SammyS]

so, I guess what I'm looking for is, can the dead battery still pass current through the right loop given that the battery on the left is charging it?

Yes, it can ... but will current pass through it with this model ? The answer should be interesting.

BTW: What were your answers for (a) and (b) ?

 

[netgypsy]

Set up the equations correctly and you don't have to guess.

 

[SammyS]

[STRIKE]Well, the bird flies a finite distance, in a finite amount of time, but does that in an infinite number of intervals ![/STRIKE]

OOPS! Wrong thread ! DUH!

Thanks gneill . My computer killed my reply & I jumped to the wrong thread to re-post.

 

[gneill]

Well, the bird flies a finite distance, in a finite amount of time, but does that in an infinite number of intervals !

Well, THAT post was a bit of a train-wreck.

 

[netgypsy]

help on the bird problem just up the list?