Density and Pressure
4 marks · EasyA container is filled with oil up to a height of 0.25 m. The density of oil is 900 kg/m³.
Calculate the pressure due to the oil at the bottom of the container (use g = 10 N/kg).
State one difference (with reason) between the pressure just below the surface and at the bottom of the oil.
Explain why the pressure caused by the liquid is the same in all directions at the same depth.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) 2250 Pa
(b) Pressure at the bottom is greater than just below the surface because pressure increases with depth.
(c) In a stationary liquid, pressure at a point acts equally in all directions.
Common mistakes: Not using correct units for height; Mixing up density and pressure
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · Recalls and substitutes values in p = hρg.
A1 (a) · 1 mark · Correct calculation of pressure in pascals. (follow-through)
B1 (b) · 1 mark · States that pressure is greater at the bottom (or increases with depth) and gives a correct reason.
B2 (c) · 1 mark · States that pressure in a liquid at a given depth acts in all directions.
Worked solution
a) Use the equation: p = h × ρ × g. h = 0.25 m, ρ = 900 kg/m³, g = 10 N/kg.
b) The pressure is greater at the bottom because pressure increases with depth (more liquid above).
c) In a stationary liquid, pressure at a point acts equally in all directions because liquid particles transmit force equally.