Battery Charger (wattage)

jesuslovesu

1. The problem statement, all variables and given/known data
http://img2.freeimagehosting.net/uploads/bf073a5eb1.png


Determine the variable resistance R if the 25 Watts to be absorbed by the battery (0.035 ohm resistor and the 10.5 V element).

2. Relevant equations
V = IR
P = IV


3. The attempt at a solution

Well I did KVL clockwise current flow
-13 + 0.02*i + iR + 0.035*i + 10.5 = 0
2.5 = 0.02i + 0.035i + iR

Then factoring in 25W=10.5*i
i = 2.381 A which is close to the answer but doesn't factor in 0.035 and I'm not sure how to do it

kamerling

The question was to compute R such that you got 25 W dissipated in the 10.5V battery. You computed what the current through this battery must be. Now use that in the equation with i and R you wrote above