Pen P of the flatbed plotter traces the curve - Path Coordinates

[Alexanddros81]

Homework Statement

This is Pytels Dynamics 2nd edition problem 13.16

13.16. Pen P of the flatbed plotter traces the curve y=x³/80000, where x and y are
measured in mm. When x=200mm, the speed of slider A is 60 mm/s. For this position, calculate
(a) the speed of P; and (b) the normal component of the acceleration of P

Homework Equations

The Attempt at a Solution

In part (a) I don't get 108.2 mm/s for the speed. what am I doing wrong?

 

[TSny]

$\dot y$ is the derivative of $y$ with respect to time. You took the derivative of $y$ with respect to $x$. Hint: chain rule.

 

[Alexanddros81]

I guess this is correct. Right?

 

[TSny]

That look's correct. Nice work.