Finding the amplitude and phase of two sinusoidal motions

[shlomo127]

Homework Statement

Determine the amplitude and phase of the resultant motion when two sinusoidal motions having the same frequency and traveling in the same direction are combined, if their amplitudes are 3.0 cm and 4.0 cm and they differ in phase by pi/2 radians.

Homework Equations

The Attempt at a Solution

I just started this Physics class and I am lost. I bought my textbook online and it still hasn't come in the mail. Can someone just point me in the right direction as to how to solve this problem, and then i'll try to solve it on my own.

Thanks so much!
Zachary

 

[Dick]

You need a trig identity. http://en.wikipedia.org/wiki/Trigonometric_identity Look at the section 'Linear combinations'.