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High School physics question is too difficult =[
A 1.0 x 10^3 kg elevator carries a maximum load of 800 kg. A constant frictional force of 4.0 x 10^3 N retards the elevator's motion upward. What minimum power, in kilowatts, must the motor deliver to lift the fully loaded elevator at a constant speed of 3.00 m/s.
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What a difficult problem.
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Problems involving work (or power, like here) are always annoying because you have be really careful about your definition of work. Here I guess they want you to include the force needed to overcome friction because they're asking for work done by the motor, not work done on the elevator.
so, recall that potential energy from height = MgH. Moving the elevator upwards at 3 m/s increases height at 3.00 m/s, and Mg is a force. force * m/s = power, and you can add the frictional force to the force of gravity. That should give you the correct answer.
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^ I think he has it. Power = ForceNeeded * Speed so just add up the force, friction and gravity, times that to speed... Don't see it as too difficult, maybe review your section abit? :D
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(1800+4000/9.81+9.81)x9.81x3=65270-65 kw :[
Without adding gravity it becomes 64981.44=65 kw
How'd you guys do it?
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=[ Yeah I don't think this is my fault. My teacher just tells me to do problems while he sits at his desk.
I did P=(1800x9.81+4000)3 P=64974 It is only 65kW =[
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Total mass of fully loaded evevator=1800kg
Power = work done/ time = (work done against friction + work done to pull the elevator up) / time taken = (1800KG*10 m/s^2*3m + 4000N*3m) / 1s = 66 kw
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Haha when you see that all the numbers are round numbers it's ok to just round off gravity to 10 m/s^2
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