Posted by Danny on Thursday, December 3, 2009 at 8:25pm.
Hi im new so maybe one of you can help me understand this question, can't find it anywhere in the book.
A person weighs 723N in air and has a bodyfat percentage of 29.3% .
What is the overall density of this person's body?
What is the volume of this person's body?
Find the apparent weight of this person when completely submerged in water?
So very confused

Physics  MathMate, Thursday, December 3, 2009 at 10:55pm
There are two formulas used for calculating bodyfat (fraction) from density:
Brozek formula: BF =(4.57/ρ4.142)
Siri formula is: BF = (4.95/ρ−4.50)
Take the inverse of the first one:
F=BF(ρ)=(4.57/ρ4.142)
R1(F)=ρ=4.57/(F+4.142)
or the Siri formula:
F=BF(ρ)=(4.95/ρ4.5)
R2(F)=ρ=4.95/(F+4.5)
For F=29.3%=0.293,
R1(F)=1.030
R2(F)=1.0327
Use the average of 1.031
Mass = 723N/9.8
=73.8 kg
Volume = mass/density
=73.8/1031 kg/m³
=0.072 m³
Apparent weight in water and neglecting density of air
= 73.8*(1.0311)= 2.3 kg.
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