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        riddles >> putnam exam (pure math) >> everone on earth
        
(Message started by: Larissa Preedy on Jun 7^th, 2005, 6:46am)

Title: everone on earth
Post by Larissa Preedy on Jun 7^th, 2005, 6:46am

Suppose that, on average, every person on earth does the equivalent of walking up a flight of stairs 117m high per day, and that, on average, each person has a mass of 99kg. If there are 5.9 billion people on earth, how much energy do all the people lolse due to their mekanical activity?

Now, i assume Ep=mgh = 99*9.81*117

from there, i multiply by 5.9billion

which is 5900000000 if i'm not mistakeN?? not sure

then, i need answer in MJ, so i mutliply by 1*10^-6

but my answer is incorrect?

i'm getting 67041245.7MJ but my answer is wrong :(

can someone tell me where i mucked up

Title: Re: everone on earth
Post by Sir Col on Jun 7^th, 2005, 7:48am

Assuming that potential energy gained by each person is equal to the mechanical energy "lost", then your method seems okay.

One person uses 99*9.81*117 = 113629.23 J of energy.
As 5.9 billion is 5900 million, we get about 5900*113629.23 = 670412457 MJ of energy used by the (modestly approximate) population of the planet.

Title: Re: everone on earth
Post by Larissa Preedy on Jun 7^th, 2005, 7:54am

ah i know, my defintion of 5.9 billion was wrong :(

wata silly mistake :( :-[