physics problem help

dafloppyone

dafloppyone

dafloppyone

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A person with mass 60 kg has an average density equal to that of water (1000kg/m3). Calculate the buoyancy force on the person if they were floating in a dense liquid with density 8000kg/m3. You may assume that g = 9.8m/s2 on Earth.

okay ive always been crap at boyancy and i dont have a scoobie how im supposed to work this out. any help is appreciated
 
if they weigh 60kg, g is ~10 and they are floating, then the buoyancy will exactly balance the weight, and will be 60g or ~600 Newtons.

Possibly not the approach they are after though...
I may have missed something in the question, unless they are trying to trick you!
 
The buoyancy force is equal to the weight of the fluid displaced, (defined by the Archimedes Principle) so is equal to rho*g*V, where rho is the density of the fluid displaced, g is the acceleration due to mavity, and V is the volume of fluid displaced.

The person is 60kg with density 1000 kg / m^3, so the volume of fluid displaced is 60 kg / 60 kg m^-3 = 0.06 m^3.

Now, F(b) = (8000 kg/m^3)(9.8 m/s^2)(0.06 m^3)
= 4704 kg m s^-2
= 4700 N (3 s.f.)
 
Last edited:
Ah, but the body wouldn't be fully submerged, it would float on the surface such that the buoyancy was only equal to his weight! ;)
 
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