Pressure in liquids and gases
4 marks · NormalA diver is swimming 15 m below the surface of a lake. The density of water is and gravitational field strength is .
Calculate the pressure due to the water at this depth.
Explain why the pressure is the same in all directions 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.
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(a) 150,000 Pa · must show Substitute p = hρg, Substitute correct values, Calculate correctly
(b) The pressure at a point in a stationary liquid acts equally in all directions because the molecules are free to move and transmit force uniformly. · must show Reference to stationary liquid, Equality of pressure in all directions, Reference to transmission of force/molecules
Common mistakes: Confusing force and pressure; Not using the correct formula for pressure in liquids
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Marking points
M1 (a) · 1 mark · Correct substitution into
A1 (a) · 1 mark · Correct answer: 150,000 Pa (follow-through)
B1 (b) · 1 mark · States pressure acts equally in all directions in a stationary liquid
B2 (b) · 1 mark · Explains why (molecules transmit force uniformly/same at a point)
Worked solution
a) Use the formula :
b) In a stationary liquid, pressure at a point acts equally in all directions because the molecules transmit force uniformly in all directions.