Calculating Work Done: Elevator Problem

[renyikouniao]

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.

 

[MarkFL]

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]

I don't know how to do this.Can you explain this for me?

 

[MarkFL]

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]

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]

Okay, do you know how to determine the gravitational potential energy of an object?

 

[renyikouniao]

Okay, do you know how to determine the gravitational potential energy of an object?

mgh?

 

[MarkFL]

Yes, good! :D

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