A Glider on an Air Track Is Connected by a Spring

Multiple Choice

A glider on an air track is connected by a spring to the end of the air track. If it is pulled $3.5 \mathrm{~cm}$ in the $-x$ direction away from its equilibrium point and then released from rest at $t=0$ , what is the initial phase $\theta$ ?

A) 0
B) $\pi / 4$
C) $\pi / 2$
D) $\pi$
E) $3 \pi / 2$
F) Some other result (specify)