physics
posted by maria .
Donald Duck and his nephews manage to sink Uncle Scrooge's yacht (m = 3527 kg), which is made of steel (ρ = 7850 kg/m^3). In typical comicbook fashion, they decide to raise the yacht (which is now on the bottom of a lake) by filling it with pingpong balls. A pingpong ball has a mass of 2.70 g and a volume of 3.35·105 m^3.
a) What is the buoyant force on one pingpong ball in water?
b) How many balls are required to float the ship?

Mg = F – mg
Mg =N• •g  N•m•g <
where M = 3527 kg,
ρ = 1000 kg/m^3 – the density of water,
V =3.35•10^5 m^3,
m =2.7•10^3 kg
N =M/(ρ•V – m) =1.15•10^5