Calculate phase between sine waves given the time difference

[exidez]

Homework Statement

How do i find the phase between sine waves knowing the time difference between each?
http://users.bigpond.net.au/exidez/sinewave.jpg

Equation for the main function is 3cos(30t - Pi/2)
The smaller sine wave is of the same frequency when is settles in a steady state.

Homework Equations

i thought it was
time difference * 2*Pi*f = phase difference in radians

The Attempt at a Solution

30 = 2*Pi * f

-.05*30 = 1.5 radians
-1.5*360/(2Pi) = -85.94 degrees

MATLAB give the phase difference as -76.3995 degrees
this is equivalent to -0.0444474274 difference in seconds

Is this just due to rounding error??

 

[exidez]

i think i just answered my own question... 2.57 seconds for the larger sine wave still give an amplitude of 3.. In this case the time difference is -0.04.

it definitely is due to rounding

 

[Redbelly98]

Homework Statement

How do i find the phase between sine waves knowing the time difference between each?
<image not shown>

Equation for the main function is 3cos(30t - Pi/2)
The smaller sine wave is of the same frequency when is settles in a steady state.

Homework Equations

i thought it was
time difference * 2*Pi*f = phase difference in radians

The Attempt at a Solution

30 = 2*Pi * f

-.05*30 = 1.5 radians
-1.5*360/(2Pi) = -85.94 degrees

MATLAB give the phase difference as -76.3995 degrees
this is equivalent to -0.0444474274 difference in seconds

Is this just due to rounding error??

You did it right, but note that the 0.05s time difference contains just one significant figure.