Monkey on a Rope
Science brain teasers require understanding of the physical or biological world and the laws that govern it.
Hanging over a pulley there is a rope, with a weight at one end. At the other end hangs a monkey of equal weight. What happens if the monkey starts to ascend the rope? Assume that the mass of the rope and pulley are negligible, and the pulley is frictionless.
Answer
The monkey is pulling down on the rope hard enough to pull itself up. This increases the tension in the rope just enough to cause the weight to rise at the same rate as the monkey, since they are of equal mass. In other words, the monkey will climb the rope and the weight will rise with him.
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Comments
od-1   
Dec 20, 2002
| I THOUGH IT WAS GOOD. WASN'T REALLY SHURE
WHAT WOULD HAPPEN. |
electronjohn  
Dec 20, 2002
| This is a great classic pulley question. I am surprised nobody ever posted before. Glad to see it here. |
curtiss82
Dec 24, 2003
| I think that the answer is wrong. If the monkey and the weight each weigh the same then the weight should remain motionless as the monkey accends up the rope. If the monkey doesn't embrace himself on an object, the maximum force that he can exert is his weight. There is no way that he can hang in mid air and pull down with a force greater than his weight. But if he plants his feet on an object, like grab on to a bar or branch, and pull, then he can exert a force greater than his weight. |
curtiss82
Dec 24, 2003
| I would like to say that I know that I may be wrong. It has been a while since I have taken a physics class that dealt with this type of material and nothing of the sort has come up in any of my engineering classes since then. |
Bobbrt
Dec 31, 2003
| Curtis, your statement "the maximum force that he can exert is his weight" is incorrect. Force is mass x acceleration. To lift himself up, the monkey has to overcome the acceleration of gravity PLUS accelerate his mass in an upward direction. If he could only exert a force equal to his weight, then he could never lift himself up. |
curtiss82
Dec 31, 2003
| Okay, that makes sense. |
Palsha
Apr 12, 2004
| You can see the same teaser at this site http://www.highiqsociety.org/common/iqtests/culturefair.htm |
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