An empty car of a roller coaster has a mass of 120 kg, one part of the track is a vertical loop with radius 11.6 m. At t

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An empty car of a roller coaster has a mass of 120 kg, one part
of the track is a vertical loop with radius 11.6 m. At the bottom
of the loop, the car has a speed of 20 m/s and at the top of the
loop it has a speed of 7.5 m/s. Calculate the work done by friction
as the car rolls from the bottom to the top of the loop.