In the below figure, PC is the connecting rod and OC is the crank making an angle $$\theta $$ with the line of stroke PO and rotates with uniform angular velocity at $$\omega $$ rad/s. The Klien's acceleration diagram for determining the acceleration of the piston P is shown by quadrilateral CQNO, the acceleration of the piston is _________ when the crank OC and connecting rod PC are at right angles to each other.