Recent content by black_squirrel

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    Prove Earth is Round: Math Equation

    yea use the formula for the surface area of a sphere 4pi*r2. Then compare it to the actual surface area of the earth. you will see that the numbers do not match proving Earth is flat :D
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    Walking on a board on frictionless surface

    okay so i guess the momentum of the center of mass would be conserved. But in the beginning, the center of mass is .5 meters from the left end of the board. When the guy walks over, the center of mass changes to 1.5 meters from the left end of the board. The left end of the board is initially at...
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    Two beakers with volatile solvents in closed system

    Homework Statement Beaker A contains a volatile solvent and beaker B contains 10% solution of a non-volatile solute in the same solvent. Both beakers are placed in a closed environment as shown. The question asks what will happen when the system has reached equilibrium. The answer is given...
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    Walking on a board on frictionless surface

    Homework Statement A 100 kg man stands on the left end of a 100 kg board 2 meters long which sits on a frictionless surface as shown. Where will the left end of the board come to rest if the man walks to the right end of the board and stops? http://pics-hosting.com/files/pexpnaxozyl1o2qins.jpg...
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    People run faster than they walk

    oh sorry. i guess what I really wanted to ask was when you say "One can assume at the top of the cycloid that the centripetal force is equal to the weight to be at the point where the foot remains on the ground and thus satisfies the condition of walking." I don't see the reasoning behind your...
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    People run faster than they walk

    oh wow, i hadn't thought of that. I'm not exactly sure what two forces you're suggesting should be equal. I'd really appreciate it if you could explain this a little bit more.
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    People run faster than they walk

    but it doesn't make sense to me to just pick an arbitrary rate. this question is wack. I'm thinking maybe if i could figure out a way of incorporating the person's weight into it...since the second part asks the speed on the moon..?
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    People run faster than they walk

    Homework Statement People can run much faster than they can walk. Why is it so? Estimate the maximal walking speed for a man, height 175 cm, and for a 7 years old child, height 120 cm. (A hint: In the first approximation, the legs of a walking person do not bend, and their length is about...
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    Planetary and atomic systems in N dimensions

    wow those are great papers but I'm having a bit of trouble following the math/physics of the second paper and the first one just kind of states Ehrenfest's findings and doesn't explain how he came at those conclusions. I'd appreciate it if you could explain it in a bit.
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    Why can't people grow infinitely tall?

    but i don't see how i can relate the weight of the person to the thickness of the muscle. that's the part that's keeping me from doing this.
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    Planetary and atomic systems in N dimensions

    Homework Statement Suppose that a human head is a sphere with the bone thickness 10% of the radius of the head. Find the fraction of the volume of the head occupied by the brain. Make a similar estimate (forget about factors of pi) in the N-dimensional space (d = N) in the limit N ->...
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    Why can't people grow infinitely tall?

    Okay so muscles strength is proportional to the square of the thickness while mass it needs to support is proportional to the cube of the thickness. Mass grows faster so there's a limit. that's clear. the question then asks: The size of some planet is 10 times greater than that of the earth...
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    Why can't people grow infinitely tall?

    This is a strange one: 1. The problem statement It is known that the strength of the muscles is proportional to the area of their section. In other words, if the muscles are two times more thick, they have four times greater strength.Explain why people cannot grow indefinitely tall...
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    Two balls falling and bouncing one off the other

    Okay, I accept that it's true but I still can't derive the expression you have written. I found the same expression listed on wikipedia on this page: http://en.wikipedia.org/wiki/Momentum#Relating_to_mass_and_velocity I'd really appreciate it if you could explain the derivation of the...
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