Finding the phase of a particle in SHM at a specific time

[Chrisemo]

Hi, I'm very confused about one question in my homework, that is due today.
I appreciate any help.Thank you very much.

1. Homework Statement
The motion of a particle is given by: x = (6.0m) cos(0.586t + 0.72)
Find the phase at time t=1.38s

2. Homework Equations
Simple harmonic motion

The Attempt at a Solution

I found the point 0.25262 m and the phase 2pi(1.38)/10.72

 

[robphy]

The "phase [angle]" is [usually] the expression inside the the cosine function: (0.586*t+0.72) radians.
So, your point is the position at t=1.38s. However, you didn't correctly identify the phase.

I say "usually" because some texts might have defined it using another function (like the sine function).

 

[Chrisemo]

thanks