Question

A 2.0cm layer of oil sits on a 5.0cm layer of water. (a) What is the pressure due to the weight of the column of oil? (b) What is the pressure due to the weight of the column of water? (c) What is the pressure due to the weight of both layers?

(Ans: (a) 157 Pa, (b) 491 Pa, (c) 648 Pa)

Answer 1

(a) The pressure the oil creates (density 800 kg/m³):

$$p_o=\rho_o g h_o=800·9.8·0.02=157\text{ Pa}$$

(b) The pressure due to the weight of the column of water:

$$p_w=\rho_wgh_w=1000·9.8·0.05=490\text{ Pa}.$$

(c) The pressure of both liquids:

$$P=p_o+p_w=647\text{ Pa}.$$