wasser@viking.DEC (John A. Wasser) (10/30/85)
> >A [massless] Rope passes over a [frictionless, massless] Pulley. On one side >is a Weight [n Kg]. On the other side, level with the Weight, is a Monkey, >also weighing n Kg. Both the Monkey and the Weight are initially at rest. >The Monkey [as you might have guessed by now] starts climbing the Rope. What >is the motion of the Weight [or for that matter, that of the Monkey]? > When the monkey pulls on the rope, the upward force applied to both the weight and the monkey is the same. Since they have the same mass they will accelerate upward together at the same rate and decelerate at the same rate due to gravity [There is a mass below them, isn't there? :-)] The result is that the weight and the monkey rise at the same rate. >What if the Pulley is not frictionless? The monkey will rise faster than the weight because some of the upward force that would be applied to the mass has been lost fighting pulley friction. At the limit of friction (infinite friction in the pulley) the weight would remain stationary as the monkey climbs. >What if the Rope is not massless? As soon as the weight starts up, the additional mass of the rope on the monkey side will cause the monkey to accelerate downward and the weight to accelerate upward. Assuming the rope is infinitely long, the weight will eventually reach the speed of light in it's upward travel and the monkey will be dropping at the same speed. At that point, if he hasn't reached the top, he never will. -John A. Wasser Work address: ARPAnet: WASSER%VIKING.DEC@decwrl.ARPA Usenet: {allegra,Shasta,decvax}!decwrl!dec-rhea!dec-viking!wasser Easynet: VIKING::WASSER Telephone: (617)486-2505 USPS: Digital Equipment Corp. Mail stop: LJO2/E4 30 Porter Rd Littleton, MA 01460