Monkey Business iii

[Ghost Post]

I agree with Crysty B, for the monkey to travel up he (or she) must apply a force down on the rope, which would put a tension in the rope which would 'travel' through the rope and apply an equal force upwards on the banana (assuming the rope does not stretch!)
Hence both would move up and meet at the top.
If you assume that the rope has a mass, as soon as the monkey applies the downward force on the rope and hence the bananas go up, there would be more rope and hence mass on the monkey's side, the pulley would turn again putting more mass on the monkey's side and the rope would keep accellerating through the pulley, so the monkey could move down if he's climbing slower than the rope is coming through the pulley. But that's a bit complicated so I'll stick with the weightless rope!!

[CrystyB]

Sorry to bother YOU with this argument, but it hit me the moment i read your post.

WHY DO WE (the physics as a science, in general) IGNORE STUFF? Because they have no real influence on the outcome. Get a rope (don't make it pretty heavy though) and see how many minutes it needs to go to fall on the floor. It's far too slow to make a big difference. Or am i just not too familiar with physics?

Oh, and before i forget [oops! i already forgotten!], Thanks for agreeing with an enemy of almoast any physics!

[This message has been edited by CrystyB (edited 05-09-2000).]

[Borodog]

I'll make this quick, as there have been a million posts on this puzzle.

1) To the people who complain about assumptions made to answer the puzzle:
TOUGH. Specify for me the mass per unit length of the rope, the coefficients of
static and kinetic friction between the rope and pulley, the same between the
pulley and its axle mounts, the pulley's moment of inertia, etc, and I could solve
the problem for you. Since the Minotaur didn't, the rope is massless and the pulley
frictionless.

2) In that case: Imagine the monkey is tied to the bananas via a rope horizontally,
say on ice (nice and frictionless). There are no external forces. The center of mass
is directly between the two. If the monkey pulls on the rope, this force is internal to
the monkey-banana system, and cannot move the center of mass. Thus the bananas
move toward the monkey just as much as the monkey moves toward the bananas,
and they will meet in the center, with the center of mass having never moved. Next,
pull on the mokey and bananas with equal and opposite forces of say, 4.9 Newtons
(that monkey was 0.5 kg, right?). The NET external force is STILL ZERO. The monkey
and bananas will STILL meet in the middle. The trick is to realise that the pulley does
absolutely NOTHING but redirect the coordinate system. Don't think 'up' and 'down,'
think 'along the rope.' The monkey and the bananas both go up, at exactly the same
rate, and meet at the pulley (as long as they were hanging at the same height originally,
which I don't particularly recall).


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Insert humorous sig here.

[CrystyB]

Borodog, THANKS for such a perfect answer.


Any solver of gl puzzles: How does minotaur decides to post answer to puzzles? The answer above shoulf put an end to everything...