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30. A 1 000-kg roller coaster car is initially at the top ofa rise, at
point . It then moves 135 ft, at an angle of 40.0° 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 poten-
tial energy of thc system when the car is at points and
B, and the change in potential energy as the car moves
between these points. (b) Repeat part (a), setting the zero
configuration with the car at point ).