00:01
So in this problem, we have the voltage in a circuit with alternating current is modeled by voltage at time t is equal to 160 times e to the power of negative 20 t times cos of 120.
00:16
Oops, not 120, 120 times pi t, where v is in volts and t greater than zero is in seconds.
00:25
Part a want to answer, what is v of zero, the initial voltage? well, v of 0 is going to equal 160 times e to the power of 0 times cos of 0, which is just going to be 160.
00:44
For b, you don't want to answer what is the frequency? so we have frequency is equal to pi, or sorry, omega over 2 pi.
00:59
Our omega is 120 pi.
01:02
We have 120 pi divided by 2 pi.
01:05
So we get 60.
01:09
We have 60 hertz or 61 over seconds, 60 oscillations per second.
01:15
Then lastly, for part c, you want to find v of t equals 100 graphically.
01:22
So i'm going to pop over to graph and calculator here...