# Buoyancy in oil/water

1. Dec 5, 2007

### ncote

1. A solid cylinder (radius = 0.150 m, height = 0.120 m) has a mass of 6.90 kg. This cylinder is floating in water. Then oil ( = 725 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?

2. (p)water(g)(V)water + (p) oil(g)(V) oil= mg
(V)water+ (V)oil= (V)cylinder
(h)oil= (V)oil/area of cylinder

3. using what i was given, i was able to calculate the area and volume of the cyclinder, which was easy enough. i know that once i use the first equation to get the volume of the oil im supposed to subtract it from the volume of the cylinder. unfortunately im not sure how to figure out the volume of the oil using the equation we were given (the first one i listed)

Last edited by a moderator: Dec 5, 2007
2. Dec 5, 2007

### Shooting Star

I can't see any drawing.

3. Dec 5, 2007

4. Dec 5, 2007

### Shooting Star

Total buoyant force upward = weight of water displaced + weight of oil displaced. Is this enough for you to proceed?

Take h as the height of the cylinder in oil. Then H-h is in water, where H is ht of cylinder. Try it out.