Which weight will lift first as the rope is pulled?

Re:Which weight will lift first as the rope is pulled? by cynicalkane on Friday September 03, 2010 @09:37AM (#1659485)

Well, the diagram is impossible unless the weights are all resting on the floor, so let's assume they are. This system will find a steady state only at a local minimum of potential energy, so the lightest weight will be lifted before the heavier two get off the ground.

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Re:Which weight will lift first as the rope is pulled? by psycocoffey on Friday September 03, 2010 @10:38AM (#1659697)

Assumptions:

  pulleys: idealized, massless, frictionless

  rope: idealized, massless, doesn't stretch

  weights: resting on ground.

As tension is applied to the rope, Weight A will be lifted first, until it is lifted to the ceiling. Then Weight B, and finally Weight A.

It helps to visualize Weight A as being massless. In that case, there would just be extra slack in the rope, and B&C would not move until the slack was taken in.

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Re:Which weight will lift first as the rope is pulled? by csmeder on Friday September 03, 2010 @08:52PM (#1661642)

Ever lower milk prices were driving a dairy farmer to desperate measures. Two years ago, he tried "Beethoven for Bovines" in his barn and milk production dropped 2%. Last year he signed up for "hex the herd" where Genuine Santa Barbara WitchesTM remotely hexed your herd for health and higher production. (The ad had said its hexes were the cause of California's improved milk production, but it didn't seem to work in Wisconsin.) So this year he drove to town to consult the ultimate power source: a theoretical physicist. The physicist listened to his problem, asked a few questions, and then said he'd take the assignment, and that it would take only a few hours to solve the problem. A few weeks later, the physicist phoned the farmer, "I've got the answer. The solution turned out to be a bit more complicated than I thought and I'm presenting it at this afternoon's Theory Seminar". At the seminar the farmer finds a handful of people drinking tea and munching on cookies---none of whom looks like a farmer. As the talk begins the physicist approaches the blackboard and draws a big circle. "First, we assume a spherical cow..."

[Clemens: QH541.15.M34 1985]

- http://www.amazon.com/gp/product/093570258X/

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Re:Which weight will lift first as the rope is pulled? by dkokelley on Friday September 03, 2010 @11:41AM (#1659925)

* Then Weight B, and finally Weight A.*

I believe you meant C, correct?

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Re:Which weight will lift first as the rope is pulled? by psycocoffey on Friday September 03, 2010 @01:31PM (#1660348)

Yes, I meant C. Too late to go and fix it now. Good catch

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Re:Which weight will lift first as the rope is pulled? by doki_pen on Friday September 03, 2010 @12:06PM (#1660023)

huh.. i didn't think of them resting on the ground and thought it was a trick question.

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