IGCSE Physics Pressure topical questions

Answer the following about pressure basics.

1. (a)Write the equation linking pressure, force and area.[1]
2. (b)State the unit of pressure.[1]
3. (c)State one way to reduce the pressure produced by a fixed force.[1]
4. (d)State one everyday example of your answer to (c).[1]

A square storage box of weight 90 N stands on a floor. Its square base has sides of 0.50 m.

1. (a)Calculate the area of the base.[1]
2. (b)Calculate the pressure the box exerts on the floor.[2]
3. (c)State the direction of the force causing this pressure.[1]

A drawing pin (thumb tack) is pushed into a noticeboard with a force of 30 N. The pin’s point has a tip area of 0.00000060 m² (6.0 × 10⁻⁷ m²).

1. (a)Calculate the pressure at the pin’s tip.[2]
2. (b)Explain why the pin enters the board but your thumb, pushing with the same force, is not harmed.[2]

A skier of weight 540 N stands on level snow. In boots, her total contact area with the snow is 0.030 m²; on skis, her total contact area is 0.60 m².

1. (a)Calculate the pressure she exerts in boots.[2]
2. (b)Calculate the pressure she exerts on skis.[1]
3. (c)Use your answers to explain why she sinks in boots but glides on skis.[1]

A uniform concrete block measures 2.0 m × 1.0 m × 0.50 m and has a weight of 24 000 N. It is laid on the ground in three different orientations.

1. (a)Calculate the greatest and the least pressure the block can exert.[3]
2. (b)Describe the orientation that gives the least pressure.[1]
3. (c)State how the block’s weight compares in the three orientations.[1]

A can is filled with a liquid. Three identical holes are punched at heights of 0.10 m, 0.20 m and 0.30 m below the liquid surface.

1. (a)State which hole produces the fastest jet, and explain why.[2]
2. (b)State what happens to each jet’s speed if the liquid is replaced by a denser liquid at the same heights.[1]
3. (c)Describe the direction in which the liquid pressure at the bottom hole pushes.[1]

A diver descends to 20 m in a lake of fresh water, density 1000 kg/m³. Take g = 9.8 N/kg and atmospheric pressure ≈ 100 kPa.

1. (a)Calculate the increase in pressure due to the water at 20 m.[2]
2. (b)Estimate the total pressure at 20 m.[2]
3. (c)The diver now swims down another 10 m. By how much does the pressure increase during that extra descent?[1]

Atmospheric pressure is about 100 kPa. A classroom door has an area of 1.8 m², and the air on both sides of the door is at this pressure.

1. (a)Calculate the force the atmosphere exerts on the door.[2]
2. (b)Explain why the door is not pushed open or crushed by this enormous force.[2]

A storage tank on a factory roof holds paraffin of density 800 kg/m³ to a depth of 1.2 m. Take g = 9.8 N/kg and atmospheric pressure = 100 kPa.

1. (a)Calculate the pressure increase due to the paraffin at the tank base. Give your answer to 2 significant figures.[2]
2. (b)Calculate the total pressure at the base.[1]
3. (c)The tank is replaced by a wider tank holding the paraffin to the same 1.2 m depth. State and explain what happens to the pressure at the base.[2]

A designer proposes a new chair. Each of its four legs ends in a pad of area 4.0 cm², and the chair plus occupant have a total weight of 1000 N, shared equally by the four legs. The carpet beneath is damaged by pressures above 2.0 MPa.

1. (a)Calculate the pressure under one leg pad.[3]
2. (b)Determine whether the carpet is damaged, and justify your answer.[1]
3. (c)Calculate the minimum pad area per leg that would keep the pressure at exactly the damage threshold.[2]

A vertical dam holds back a reservoir of fresh water (density 1000 kg/m³). The water is 30 m deep against the dam. Take g = 9.8 N/kg.

1. (a)Explain why the dam is built thicker at its base.[2]
2. (b)Calculate the water pressure increase at the base of the dam.[2]
3. (c)A valve is opened at a depth of 10 m. Calculate the pressure increase there and state how it compares with the base value.[2]

A swimming pool has a vertical window panel of area 0.50 m² set into its wall. The centre of the panel is 2.0 m below the water surface. Water has density 1000 kg/m³ and g = 9.8 N/kg.

1. (a)Calculate the pressure increase due to the water at the centre of the panel.[2]
2. (b)Calculate the force the water exerts on the panel, using the pressure at its centre.[2]
3. (c)The pool is refilled so the panel’s centre is 2.5 m below the surface. Calculate the new force on the panel.[2]