What is the tangential acceleration?

The slider P in the figure is sliding up along a vertical pole at a constant velocity of u m/s. The slider Q slides on the horizontal rod connected to P and is also constrained to move along a circular track of radius R = 500 mm as shown.

What is the tangential acceleration (in m/s2) of Q when P is at y = 200 mm.

The help notes for 2.22 may be helpful. There, you were given an expression for a(t). Here, you are given V(t). This is the velocity of the slider Q. The y- component of the VQ is the same as u. The x-component can be expressed in terms of teta, VP, y, and R.

u[m/s] = 14.1;

http://micko.dyndns.org/pq_slide.jpg