The rod $O A$ is held at the constant angle $\beta=30^{\circ}$ while it rotates about the vertical with a constant angular rate $\dot{\theta}=120$ rev/min. Simultaneously, the sliding ball $P$ oscillates along the rod with its distance in millimeters from the fixed pivot $O$ given by $R=200+50 \sin 2 \pi n t,$ where the frequency $n$ of oscillation along the rod is a constant 2 cycles per second and where $t$ is the time in seconds. Calculate the magnitude of the acceleration of $P$ for an instant when its velocity along the rod from 0 toward $A$ is a maximum.