Change in potential energy on a roller coaster drop (frictionless)

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800 kg roller coaster is initially at the top of a rise, at point A. It then moves 125 ft (38.1 m), at an angle of 40.0° below the horizontal, to a lower point, B.

(a) Choose point B to be the zero level for gravitational potential energy. Find the potential energy of the roller coaster-Earth system at points A and B and the change in potential energy as the coaster moves.

To start, I aimed to find the potential energy at point A:
Ug = mgh
Ug = (800)(9.8)(y component of h)
Ug = (800)(9.8)(38.1sin40)
Ug = 222561.92 J

What am I missing in my process? Thanks in advance.
 

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  • #2
Doc Al
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Everything looks good except your final answer. Redo that calculation.
 
  • #3
LowlyPion
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800 kg roller coaster is initially at the top of a rise, at point A. It then moves 125 ft (38.1 m), at an angle of 40.0° below the horizontal, to a lower point, B.

(a) Choose point B to be the zero level for gravitational potential energy. Find the potential energy of the roller coaster-Earth system at points A and B and the change in potential energy as the coaster moves.

To start, I aimed to find the potential energy at point A:
Ug = mgh
Ug = (800)(9.8)(y component of h)
Ug = (800)(9.8)(38.1sin40)
Ug = 222561.92 J

What am I missing in my process? Thanks in advance.
I think your vertical drop calculation is in error. Your answer suggests the original height was 44.1m when the problem says it was 38.1m
 

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