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Calculating Work Done: Elevator Problem

renyikouniao

Member
Jun 1, 2013
41
An elevator cabin which weighs 3000 lb is lifted up 120 feet. It is connected with a counterweight of 3200 lb by a cable of length 200 feet weighing 4 lb per feet.

What work is done (or gained) if

a) the counterweight comes to rest at the same position as original position of the cabin,

b) 20 feet below the original position of the cabin.

Assume that the circumference of the turning wheel of the cable is 10 feet.
 
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MarkFL

Administrator
Staff member
Feb 24, 2012
13,775
I would use the work-energy theorem here. The change in energy will be the amount of work done. Can you compute $\Delta E$?
 

renyikouniao

Member
Jun 1, 2013
41
I don't know how to do this.Can you explain this for me?
 

MarkFL

Administrator
Staff member
Feb 24, 2012
13,775
First let me ask if this is for a physics course or for a calculus course...i.e., are you expected to do this dynamically or are you allowed to use energy considerations. Have you recently been studying gravitational potential energy?
 

renyikouniao

Member
Jun 1, 2013
41
It's calculus,yes we can use physics equations.And I do know some..But I don't know where to begin.
First let me ask if this is for a physics course or for a calculus course...i.e., are you expected to do this dynamically or are you allowed to use energy considerations. Have you recently been studying gravitational potential energy?
 

MarkFL

Administrator
Staff member
Feb 24, 2012
13,775
Okay, do you know how to determine the gravitational potential energy of an object?
 

renyikouniao

Member
Jun 1, 2013
41

MarkFL

Administrator
Staff member
Feb 24, 2012
13,775
Yes, good! :D

So where do you think would be an appropriate place to orient the origin of our coordinate axis?