**1. The problem statement, all variables and given/known data**

Here is the question along with the solution. I am mainly concerned about part b).

**2. Relevant equations**

See image above.

**3. The attempt at a solution**

So instead, I decided to try to find the answer using the following formula:

P_{in} = P_{i^2 r} + P_{Bm} + P_{out}

This results in:

V_{a}(I_{a}+I_{f}) = I_{a}^2 R_{a} + I_{f}^2 R_{f} + 0.05P_{out} + P_{out}

Solving the above results in T_{m} = 10.461 which is slightly off compared to the actual solution, does anyone know why?

http://ift.tt/1cnJnSV