# Homework Help: Need help finding the Max Power in a math/EE problem please

1. Mar 25, 2016

### DominoK

1. The problem statement, all variables and given/known data
The voltage across the inductor is given by v(t)=L(di(t)/dt).
Determine:

(1.) Tthe voltage v(t)
(2.) The power p(t)=v(t)*i(t).
(3.) The maximum power transferred ( t = ??? (in seconds) when power is at maximum).

if the inductance is L=2 and the current i(t) is given by:

(a.) i(t)=13e-200t A.
(b.) i(t)=20cos(2π60t) A.

It's the formula/steps to get pmax that I am stuck on.

Thank you so much!

2. Relevant equations
See above.

3. The attempt at a solution

I got as far as answering the (1.) and (2.) for each (a.) and (b.), but I do not know how to calculate the pmax.

(a1.) v(t) = -5.2 e-200t V.
(a2.) p(t) = -67.6 e-400t W.
(a3.) ??? ( t = ??? when power is at maximum).

(b1.) v(t) = -4.8 π sin(120πt) V.
(b2.) p(t) = -48sin(240πt) W.
(b3.) ??? ( t = ??? when power is at maximum).

Thank you very much!!!

2. Mar 25, 2016

### Staff: Mentor

What's the behavior of y = e-400t? This is a decaying exponential function, which tells you something about where its maximum value is.

The negative sign on -67.6 looks wrong to me. Power should be nonnegative, I believe.
What does the graph of y = sin(240πt) look like? What is its maximum value, and where does it attain this maximum? Also, I'm not sure about the sign you have on -48.