Density and Pressure
4 marks · NormalA diver descends to a depth of 25 m in the sea. The density of seawater is 1050 kg/m³.
Calculate the increase in pressure on the diver at this depth due to the water alone. Use g = 10 N/kg. Give your answer in kPa.
State and explain why the pressure inside the diver's air tank must be greater than the pressure at this 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) 262.5 kPa · must show Correct substitution, Unit converted to kPa
(b) Because if the pressure inside the tank is not greater than the external pressure, water would enter the tank (or breathing would be impossible). The air needs to come out despite outside pressure. · must show States reason for higher internal pressure, Explanation relates to equalising or overcoming outside pressure
Common mistakes: Using atmospheric pressure for increase instead of just water; Unclear explanation for tank pressure
Show mark scheme and worked solution
Marking points
M1a (a) · 1 mark · Substitutes correct values into p = h × ρ × g
A1a (a) · 1 mark · Final answer correctly converted to kilopascals (kPa)
B1b (b) · 1 mark · States the pressure in the tank must be higher than the external pressure
B2b (b) · 1 mark · Explains this is so air leaves the tank or water does not enter (clear physical reason)
Worked solution
b) The pressure inside the tank must be greater so air can come out for breathing. If the external pressure were greater than the tank, water would enter the tank or air could not leave for breathing.