A $900-$kg roller coaster car is initially at the top of a rise, at point $.$ It then moves $165$ ft$,$ at an angle of $40\mathrm{.}0$ below the horizontal, to a lower point $.$

$($a$)$ Choose the car at point to be the zero configuration for gravitational potential energy of the roller coaster$$Earth system. Find the potential energy of the system when the car is at points and $,$ and the change in potential energy as the coaster moves between these points.

at point Jat point Jchange in potential energy J

$($b$)$ Repeat part $($a$),$ setting the zero configuration with the car at point

at point Jat point Jchange in potential energy