In the design of a control mechanism, the vertical slotted guide is moving with a constant velocity $\dot{x}=15$ in./sec during the interval of motion from $x=-8$ in. to $x=+8$ in. For the instant when $x=6$ in. calculate the $n$ - and $t$ -components of acceleration of the pin $P,$ which is confined to move in the parabolic slot. From these results, determine the radius of curvature $\rho$ of the path at this position. Verify your result by computing $\rho$ from the expression cited in Appendix C/10.