A column of mercury (S.G.13) is twice the height of a column of water. What is the difference in pressure at the bottom of the mercury column in comparison with the column of water?

a) the same

b) twice as great

c) 13 times as great

d) 26 times as great

**Explanation**

The formula for pressure at the bottom of a column of fluid is P=ρgh where ρ is the fluid density. Specific gravity is the ratio of fluid density to water density. Since the mercury is 13 times as dense as water and the column is twice as tall, the pressure will be 26 times as great.

a) the same, incorrect, Pressure at the bottom of a column of fluid depends on the fluid density and height of the column.

b) twice as great, incorrect, This answer neglects the difference in specific gravity.

c) 13 times as great, incorrect, This answer choice neglects the doubled height of the mercury column.

d) 26 times as great, correct.