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September 19th, 2013, 06:31 PM  #1 
Newbie Joined: Sep 2013 Posts: 1 Thanks: 0  Person weighs 100kg at 2 metres, how much at 4m?
I was presented this question and I am extremely interested to find out how to formulate it. It goes: A man weighing 100kg at a hight of 2 metres grew to 4 metres with the same body proportions, how much does he weigh now? 
September 19th, 2013, 08:08 PM  #2 
Senior Member Joined: Jul 2010 From: St. Augustine, FL., U.S.A.'s oldest city Posts: 12,211 Thanks: 520 Math Focus: Calculus/ODEs  Re: Person weighs 100kg at 2 metres, how much at 4m?
Since his measures double in all three dimensions of space, his mass would increase by a factor of 8.

September 19th, 2013, 10:27 PM  #3 
Senior Member Joined: Jun 2013 From: London, England Posts: 1,316 Thanks: 116  Re: Person weighs 100kg at 2 metres, how much at 4m?
Who comes up with these questions? I mean, how many people grow to 4m? One interesting point is that the BMI (Body Mass Index) which attempts to measure whether someone is overweight or underweight divides the person's weight by the square of their height. Not the cube of their height. I'm not sure whether this means that the other dimensions do not grow in proportion to height. 
September 19th, 2013, 10:51 PM  #4 
Senior Member Joined: Jul 2010 From: St. Augustine, FL., U.S.A.'s oldest city Posts: 12,211 Thanks: 520 Math Focus: Calculus/ODEs  Re: Person weighs 100kg at 2 metres, how much at 4m?
When you gain weight, you typically only "grow" in two of the three dimensions...i.e., you do not get taller.

September 19th, 2013, 11:40 PM  #5 
Math Team Joined: Jul 2011 From: North America, 42nd parallel Posts: 3,372 Thanks: 233  Re: Person weighs 100kg at 2 metres, how much at 4m?
I always wonder why the wieght is popularly given in kg , it should be in Newtons. What is the scale really measuring? If it's measuring Newtons then the reading of 100 kg actually corresponds to a mass of 10.2 kg. If it's 'magically' measuring mass of 100 kg then the weight would have to be 981 Newtons. It's a no win situation because W = mg , not just m alone. What do you think about that? 
September 19th, 2013, 11:46 PM  #6 
Senior Member Joined: Jul 2010 From: St. Augustine, FL., U.S.A.'s oldest city Posts: 12,211 Thanks: 520 Math Focus: Calculus/ODEs  Re: Person weighs 100kg at 2 metres, how much at 4m?
I was once stopped by a policeman for blasting my new car stereo too loud, and he asked for my height/weight, which I gave in meters and Newtons...he was not impressed. Most people seem to equate mass and weight, thinking only about existence here on the surface of the Earth, where the constant of proportionality between the two remains more or less constant. 
September 20th, 2013, 12:11 AM  #7  
Math Team Joined: Jul 2011 From: North America, 42nd parallel Posts: 3,372 Thanks: 233  Re: Person weighs 100kg at 2 metres, how much at 4m? Quote:
"Thank's for the ticket officer, oh by the way , you're 6.2 SLUGS"  
September 20th, 2013, 12:24 AM  #8  
Senior Member Joined: Jun 2013 From: London, England Posts: 1,316 Thanks: 116  Re: Person weighs 100kg at 2 metres, how much at 4m? Quote:
 
September 21st, 2013, 05:05 AM  #9  
Math Team Joined: Jul 2011 From: North America, 42nd parallel Posts: 3,372 Thanks: 233  Re: Person weighs 100kg at 2 metres, how much at 4m? Quote:
Living in the pools, They soon forget about the sea...— Rush, "Natural Science" (1980)  

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