posted by Amanda on .
A hollow plastic sphere is held below the surface of a freshwater lake by a cord anchored to the bottom of the lake. The sphere has a volume of 0.600m^3 and the tension in the cord is 840N . What is the mass of the sphere?
is this how i would find the mass?
and to find the buoyant force exerted by the water on the sphere.
please just tell me if im on the right track
Your buoyant force is
Fb = (water density)(volume)x g,
but the water density in SI units is 1000 kg/m^3, not 1. So Fb = 5886 N
If the mass of the sphere is M g, a vertical force balance requires that
M*g + T = Fb
M = (1000kg/m^3*0.6*m^3*g - 840 N)/g
= 600 kg - 840/g = 514 kg