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Homework Statement
The current through a resistor is i(t) = 2sin(30t + 169°), and R = 50Ω
What is the power dissipated by R at t = 3.7ms?
Homework Equations
p = i2R
or
p = .5(Vmax)(Imax)*(cos([tex]\phi[/tex]-[tex]\theta[/tex])+cos(2*[tex]\omega[/tex]*t+[tex]\phi[/tex]+[tex]\theta[/tex]))
The Attempt at a Solution
I feel stupid for asking this but I just can't get the numbers right. I think this is a situation where the problem is so easy that it is difficult... anyway
i(t) = 2*sin(30t + 169°) = 2*cos(30t + 169°-90°)= 2*cos(30t + 79°)
so
p = i2R = (2*cos(30t + 79°))2*50= 4*50*(cos(30t + 79°))2
if t = 3.7ms = .0037s
4*50*(cos(30*.0037 + 79°))2 = 7.1372 Watts
the actual answer is 1.31 Watts and I can't get this right. I must be making a stupid mistake somewhere that is so simple that I just can't see it. I also get my answer if I use the second formula I listed. Where is my mistake?
Thanks!