Practise Pressure with depth and upthrust. 15 exam-style questions plus unlimited generated ones on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
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Calculate the pressure due to a column of water 2.0 m high. density of water = 1000 kg/m3 gravitational field strength = 9.8 N/kg Use the equation: pressure = height of the column × density of the liquid × gravitational field strength
19 600 Pa
Complete the sentence. The pressure of a liquid on the bottom surface of a submerged object is ............ than the pressure on its top surface.
Greater.
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy4 marks
(a) How does the pressure in a liquid change as the depth increases? Tick (✓) one box.[1]
It decreases
It increases
It stays the same
(b) Calculate the pressure due to a column of water 2.0 m high. density of water = 1000 kg/m3 gravitational field strength = 9.8 N/kg Use the equation: pressure = height of the column × density of the liquid × gravitational field strength[2]
(c) What is the name of the upward force that a liquid exerts on an object that is partly or completely submerged in it?[1]
Show the answer and mark scheme
(a)Answer: It increases
(b)Answer: 19 600 Pa
p = 2.0 × 1000 × 9.8
19 600 (Pa)
(c)Answer: Upthrust.
upthrust
Question 2Medium8 marks
A swimming pool is 2.5 m deep at the deep end. density of water = 1000 kg/m3 gravitational field strength = 9.8 N/kg
(a) Calculate the pressure caused by the water at the bottom of the deep end. Use the Physics Equations Sheet.[2]
(b) Explain why the pressure in the water increases with depth.[2]
(c) Calculate the difference in pressure between a point 0.50 m below the surface of the water and a point 2.0 m below the surface.[2]
(d) A second pool of the same depth is filled with sea water. Sea water has a greater density than fresh water. Explain how the pressure at the bottom of this pool compares with the pressure at the bottom of the first pool.[2]
Show the answer and mark scheme
(a)Answer: 24 500 Pa
p = 2.5 × 1000 × 9.8
24 500 (Pa)
(b)Answer: The deeper the point, the taller the column of water above it, so the greater the weight of water pressing on each unit area.
the height of the column of water above a point increases (with depth)
so the weight of water above (each unit area) increases
(c)Answer: 14 700 Pa
Δp = (2.0 − 0.50) × 1000 × 9.8
14 700 (Pa)
(d)Answer: It is greater, because the same height of denser water has a greater weight (p = hρg).
the pressure is greater
because a column of sea water of the same height has a greater weight / pressure is proportional to the density of the liquid
Question 3Hard8 marks
Objects placed in water experience an upthrust. Some objects float and some objects sink.
(a) Explain why an object that is submerged in water experiences an upthrust, and describe the factors that determine whether the object floats or sinks.[6]
(b) A boat floats higher in sea water than in fresh water. Explain why.[2]
Show the answer and mark scheme
(a)
pressure in a liquid increases with depth (p = hρg)
the bottom surface of the object is deeper than the top surface, so the pressure on the bottom surface is greater
force = pressure × area, so the upward force on the bottom surface is greater than the downward force on the top surface
the resultant upward force is the upthrust; the horizontal forces on the sides cancel
the upthrust is greater if more of the object is below the surface / if the liquid is denser
an object sinks if its weight is greater than the upthrust when it is completely submerged (its density is greater than the density of the liquid)
an object floats if the upthrust becomes equal to its weight before it is completely submerged (its average density is less than that of the liquid)
hollow objects such as ships float because their average density is low
Marked with levels of response: the full level descriptors are in the app.
(b)Answer: Sea water is denser, so less of the boat must be submerged to give an upthrust equal to its weight.
sea water is denser than fresh water / the pressure at a given depth is greater in sea water
so a smaller volume of the boat needs to be submerged to produce an upthrust equal to the boat’s weight