Physics question?

Question

1. An ice cube is placed in a glass of water. The cube is 2.0 cm on each side and has a density of 0.917 g/cm3. What is the magnitude of the buoyant force on the ice?


2. An object weighs 315 N in air. When tied to a string, connected to a balance, and immersed in water, it weighs 265 N. When it is immersed in oil, it weighs 269 N. Find the following:
a)the density of the object
b)the density of the oil

Answer 1

1. (0.917 g/cm^3)*(9.8m/s^2)*(2.0cm)^3 = 72N

2. Take the air density to be 1.2 g/L = 1.2mg/ml, and water density to be 1.0 g/ml.
Let V (ml) be the volume and X (g/ml) be the density, of the object. We have:
V*X - V*1.2x10^-3 = 315N...(1)
V*X - V* 1.0 = 265N.............(2)
(1)-(2):
V = 50 (cm^3)
Substitute into (2), we have:
X = 6.3
Hence the density of the object is 6.3 g/cm^3.

V*X - V*(density of the oil) = 269N
(density of the oil) = 0.92 (g/ml)