In: Physics
A solid cylinder (radius = 0.190 m, height = 0.190 m) has a mass of 21.4 kg. This cylinder is floating in water. Then oil (ρ = 867 kg/m3) is poured on top of the water until the situation shown in the drawing results. How much of the height of the cylinder is in the oil?
Without the drawing, I will assume that the axis of revolution
of the cylinder is pointing up. That makes the volume of the
submerged cylinder proportional to the height submerged.
There is a bouyant force due to the oil, and another buoyant force
due to the water. Their sum is equal to the weight of the
cylinder.
Bo + Bw = W
po*g*Vo + pw*g*Vw = pc*g*Vc
po*Vo + pw*Vw = pc*Vc
po*(Vo/Vc) + pw*(Vw/Vc) = pc
where:
Vo, Vw, Vc = volume of cylinder in oil, in water, total volume of
cylinder
po, pw, pc = density of oil, water, cylinder
Further, the portions in oil and water make up the whole, so we
have
(Vo/Vc) + (Vw/Vc) = 1
We now have a system of equations, and the solution is
volume of cylinder pi *r2 * h = 3.14 * (0.190)2 * 0.190 = 0.0215m3
density pc=mass/volume = 21.4 kg/0.0215m3 =993.62
Kg/m3 ,pw=1000kg/m3
(Vo/Vc) = (pc - pw)/(po - pw)= 0.0479
(Vw/Vc) = (po - pc)/(po - pw)=0.952
Thus height of cylinder is in the oil =Vo/Vc * height = 0.0479*
0.19 = 0.0091 m is in the oil.