A roller coaster starts out at rest on the first rise --- 20 meters above the low point of the track. How fast is it moving when it gets to the low point?
Start ------- E = m(10m/s )(20m) = m(200m/s).

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A roller coaster starts out at rest on the first rise --- 20 meters above the low point of the track. How fast is it moving when it gets to the low point?
Start ------- E = m(10m/s )(20m) = m(200m/s).
Low point. --- E = (1/2)mv.
Set the two expressions equal to each other and solve.

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Start ------- E = m(10m/s )(20m) = m(200m/s).
Low point. --- E = (1/2)mv.

Set the two expressions equal to each other:
--- m(200m/s) = (1/2)mv
Notice that the mass is on both sides and divide by it
--- (200m/s) = (1/2)v
--- 400m/s = v. ======> Find v = 20m/s.

Notice that the answer would be the same if the roller coaster fell straight down off the track.

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