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Pressure in fluids: GCSE Combined Science Physics practice questions

Foundation and Higher · Grade 6

A second set of questions on pressure in fluids. They are different from the ones on the topic page. Try each, then open the answer and compare your working.

More questions

Question 1 Hard

The pressure caused by water is 45 000 Pa. Work out the depth. Water has a density of 1000 kg/m³ and g = 10 N/kg.

Show answer

Answer: 4.5 m

  1. h = p ÷ (ρ × g)
  2. 45 000 ÷ 10 000 = 4.5 m

Question 2 Hard

Explain why atmospheric pressure is lower at the top of a mountain.

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Answer: There is less air above, so the weight of air and the pressure are lower.

  1. Pressure comes from the weight of air above.
  2. There is less air above, so the pressure is lower.

Question 3 Hard

A block with a weight of 12 N floats on water. State the upthrust on it and explain your answer.

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Answer: 12 N, because the forces are balanced so the upthrust equals the weight.

  1. The block is not moving up or down.
  2. The forces are balanced, so the upthrust equals the weight, 12 N.

Question 4 Hard

Work out the pressure caused by water at a depth of 10 m. Water has a density of 1000 kg/m³ and g = 10 N/kg.

Show answer

Answer: 100 000 Pa

  1. p = hρg
  2. 10 × 1000 × 10 = 100 000 Pa

Quick checks

Short questions with options. Choose one before you open the answer.

Check 1

What is pressure?

  1. the force acting on each unit of area
  2. the total force on an object
  3. how heavy an object is
Show answer

the force acting on each unit of area Pressure tells you how concentrated a force is.

Check 2

What is the equation for pressure?

  1. pressure = force × area
  2. pressure = force ÷ area
  3. pressure = area ÷ force
Show answer

pressure = force ÷ area p = F ÷ A, with force in newtons and area in square metres.

Check 3

What is the unit of pressure?

  1. the newton, N
  2. the joule, J
  3. the pascal, Pa
Show answer

the pascal, Pa Pressure is measured in pascals.

Check 4

What is one pascal in other units?

  1. one newton per square metre
  2. one newton per metre
  3. one joule per second
Show answer

one newton per square metre 1 Pa = 1 N/m².

Check 5

The same force acts on a smaller area. What happens to the pressure?

  1. It gets bigger.
  2. It gets smaller.
  3. It stays the same.
Show answer

It gets bigger. Dividing the same force by a smaller area gives a bigger number.

Check 6

Why do snowshoes stop you sinking into snow?

  1. They make you weigh less.
  2. They spread your weight over a bigger area, so the pressure is smaller.
  3. They make the snow harder.
Show answer

They spread your weight over a bigger area, so the pressure is smaller. Bigger area means smaller pressure for the same weight.

Check 7

Why does a sharp knife cut better than a blunt one?

  1. A sharp knife is heavier.
  2. A sharp knife has a bigger area.
  3. The edge has a small area, so the same force gives a big pressure.
Show answer

The edge has a small area, so the same force gives a big pressure. The sharp edge concentrates the force.

Check 8

A force of 90 N acts on an area of 0.3 m². What is the pressure?

  1. 300 Pa
  2. 27 Pa
  3. 0.0033 Pa
Show answer

300 Pa 90 ÷ 0.3 = 300 Pa.

Check 9

A pressure of 5000 Pa acts on an area of 0.2 m². What is the force?

  1. 25 000 N
  2. 1000 N
  3. 5000.2 N
Show answer

1000 N force = pressure × area = 5000 × 0.2 = 1000 N.

Check 10

An area is 500 cm². What is it in m²?

  1. 5 m²
  2. 5000 m²
  3. 0.05 m²
Show answer

0.05 m² Divide by 10 000 to change cm² to m².

Check 11

In which directions does pressure in a liquid act?

  1. in all directions, at right angles to surfaces
  2. downwards only
  3. upwards only
Show answer

in all directions, at right angles to surfaces A liquid pushes on the sides, top and bottom of anything in it.

Check 12

Why does pressure in a liquid increase with depth?

  1. The liquid gets hotter as you go down.
  2. There is more liquid above pressing down.
  3. The liquid gets lighter as you go down.
Show answer

There is more liquid above pressing down. Deeper means a taller column of liquid above you.

Check 13

Write the equation for pressure in a liquid. (Higher tier)

  1. pressure = height × density × gravitational field strength
  2. pressure = height ÷ density
  3. pressure = force ÷ height
Show answer

pressure = height × density × gravitational field strength p = h × ρ × g.

Check 14

What is the density of water in kg/m³?

  1. 1000
  2. 1
  3. 100
Show answer

1000 Water has a density of 1000 kg/m³, or 1 g/cm³.

Check 15

Water at a depth of 3 m. What is the pressure? Take g = 10 N/kg. (Higher tier)

  1. 3000 Pa
  2. 300 Pa
  3. 30 000 Pa
Show answer

30 000 Pa p = 3 × 1000 × 10 = 30 000 Pa.

Check 16

The pressure from water is 20 000 Pa. What is the depth? Take g = 10 N/kg. (Higher tier)

  1. 2 m
  2. 20 m
  3. 200 000 000 m
Show answer

2 m h = 20 000 ÷ (1000 × 10) = 2 m.

Check 17

What causes upthrust?

  1. The pressure on the bottom of an object is greater than on the top.
  2. The object is lighter than water.
  3. Air pushes the object upwards.
Show answer

The pressure on the bottom of an object is greater than on the top. The bottom is deeper, so the upward push is bigger than the downward push.

Check 18

What is the size of the upthrust on an object?

  1. the weight of the object itself
  2. the weight of the fluid it pushes out of the way
  3. the volume of the object
Show answer

the weight of the fluid it pushes out of the way Upthrust equals the weight of the displaced fluid.

Check 19

When does an object float?

  1. when its weight equals the upthrust
  2. when its weight is bigger than the upthrust
  3. when it has no weight
Show answer

when its weight equals the upthrust Balanced forces mean it floats still.

Check 20

A block with a weight of 12 N floats still. What is the upthrust on it?

  1. 0 N
  2. 24 N
  3. 12 N
Show answer

12 N Floating still means the forces are balanced, so upthrust = weight.

Check 21

A student says a ship floats because steel is light. What is wrong?

  1. A ship is heavy. It floats because it pushes aside enough water to give an upthrust equal to its weight.
  2. Steel is lighter than water.
  3. Water pushes down on the ship to hold it up.
Show answer

A ship is heavy. It floats because it pushes aside enough water to give an upthrust equal to its weight. A wide hull moves a lot of water aside.

Check 22

What causes atmospheric pressure?

  1. air particles colliding with surfaces, or the weight of the air above
  2. the Sun pushing on the air
  3. the Earth's magnetic field
Show answer

air particles colliding with surfaces, or the weight of the air above Gas particles are always moving and hitting things.

Check 23

Why is the air pressure lower at the top of a mountain?

  1. The air at the top is hotter.
  2. There is less air above, so the air is thinner.
  3. There is more air above at the top.
Show answer

There is less air above, so the air is thinner. Fewer particles collide with each surface.

Check 24

Why does a sealed crisp packet puff up on a plane?

  1. The air pressure outside falls, so the air inside pushes the packet outwards.
  2. The crisps get bigger.
  3. The packet is heated by the engines.
Show answer

The air pressure outside falls, so the air inside pushes the packet outwards. The inside pressure is now bigger than the outside pressure.

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