2023 THREE(c)

Char goes for a ride on a Ferris wheel. As she rotates around,
her position can be described by the pair of parametric
equations :

$x=5\sqrt{2}\sin \left(\frac{\pi t}{5}\right)$ and $y=10-5\sqrt{2}\cos \left(\frac{\pi t}{5}\right)$

where $t$ is time, in seconds, from the start of the ride.

Find the gradient of the normal to this curve at the point when
$t=6.25$ seconds, after the start of the ride.

*You must use calculus and show any derivatives that you need
to find when solving this problem.*