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Phy 231
Your 'cq_1_21.2' report has been received. Scroll down through the document to see any comments I might have inserted, and my final comment at the end.
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A typical automobile coasts up a typically paved incline, stops, and coasts back down to the same position.
When it reaches this position, is it moving faster, slower or at the same speed as when it began? Explain
answer/question/discussion: ->->->->->->->->->->->-> scussion:
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It is moving slower than when it began.
It starts off with KE and a particular velocity, then experiences a decrease in both as it coasts uphill, slowing until it comes to a stop.
It loses KE (and speed) through several types of work: the work against the conservative force of gravity (the component of gravity parallel to the incline), and work against nonconservative forces including air resistance and friction.
The work against gravity results in a corresponding increase in gravitational PE as it climbs the hill. However, it doesn't regain in the form of PE all the KE it has lost, so when it begins to roll back downhill, the total PE is less than the KE it started with.
Then, as it rolls back down, gravity does work on it, causing it to accelerate downhill. But friction and air resistance are also doing work on it, causing it to accelerate less than it would have otherwise. So it does not have the chance to get back to the speed it began with.
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10 minutes
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Very good.
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