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Old Oct 11th 2009, 01:29 PM   #1
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Elevator Problem

A 651 kg elevator starts from rest and moves upward for 3.10 s with constant acceleration until it reaches its cruising speed, 1.67 m/s.
a. What is the average power of the elevator motor during this period?
b. How does this amount of power compare with its power during an upward trip with constant speed?

My attempt at this problem has to first been to find the acceleration using the time and velocity and then using the acceleration to find the sum of the forces. Then I tried to use that to find the distance traveled and eventually the power. I am really confused about this problem so can someone please help. Thanks!
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Old Oct 12th 2009, 03:03 AM   #2
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Use the fact that power = force x velocity, which can be obtained by dividing the eqn work = force x displacement on both sides by time.

Thus avg power = force x avg vel.

When finding the force, we need to remember


Fnet = Fapplied - mg
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