1. The problem statement, all variables and given/known data An air-track glider attached to a spring oscillates with a period of 1.50 s. At t=0s, the glider is 5.60 cm left of the equilibrium position and moving to the right at 40.6 cm/s. What is the phase constant? 2. Relevant solutions 3. The attempt at a solution [tex]T=1.50s[/tex] [tex]\omega=2\pi/T=4.189[/tex] [tex]1: A cos \phi =-0.056m[/tex] [tex]2: -\omega A sin \phi =0.406m/s[/tex] [tex]-A sin \phi=0.406/4.189=0.097[/tex] Divide equation 2 by equation 1: [tex] - tan \phi=0.097/-0.056[/tex] [tex]\phi=1.05 rad[/tex] However, the correct answer is exactly twice my answer, and also negative of what I got. Can anyone explain what dumb mistake I'm making here? Thanks!