Course: Separate Physics only | Tier: Foundation + Higher | Equation sheet: given in the exam
The equation
pressure = force normal to a surface ÷ area of that surface p = F / A
| Quantity | Symbol | Unit |
|---|---|---|
| pressure | p | pascals (Pa) |
| force | F | newtons (N) |
| area | A | square metres (m²) |
Rearranged: F = p × A | A = F ÷ p | 1 cm² = 0.0001 m²
Use FIFA for every answer
- F – Formula: write the equation as it appears on the sheet.
- I – Insert: put in the numbers (convert to standard units first).
- F – Fix: rearrange to make the unknown the subject.
- A – Answer: calculate and always give the unit.
Foundation: aim for Q1–8. Higher: aim for Q4–10. Most questions need rearranging.
Questions
Q1 (F) A packing crate weighing 600 N rests on a floor over an area of 1.5 m². Calculate the pressure on the floor.
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F: p = F / A
I: p = 600 ÷ 1.5
F: p is already the subject – no rearranging needed
A: 400 Pa
Q2 (F) A car tyre presses on the road with a pressure of 200 000 Pa over an area of 0.02 m². Calculate the force on the road from this tyre.
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F: p = F / A
I: 200 000 = F ÷ 0.02
F: F = 200 000 × 0.02
A: 4000 N
Q3 (F) A walker weighing 700 N wears snowshoes. The pressure on the snow is 2800 Pa. Calculate the total area of the snowshoes.
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F: p = F / A
I: 2800 = 700 ÷ A
F: A = 700 ÷ 2800
A: 0.25 m²
Q4 (F) One of an elephant’s feet pushes on the ground with a force of 12 000 N and a pressure of 80 kPa. Calculate the area of the foot.
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Convert first: 80 kPa = 80 000 Pa
F: p = F / A
I: 80 000 = 12 000 ÷ A
F: A = 12 000 ÷ 80 000
A: 0.15 m²
Q5 (F) A loaded tractor exerts a pressure of 50 kPa on soil. Its tyres have a total contact area of 2.4 m². Calculate the weight of the tractor in kN.
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Convert first: 50 kPa = 50 000 Pa
F: p = F / A
I: 50 000 = F ÷ 2.4
F: F = 50 000 × 2.4 = 120 000 N
A: 120 kN
Q6 (F/H) A person standing on both feet exerts 20 kPa on the floor. Each trainer has a contact area of 150 cm². Calculate the person’s weight.
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Convert first: total area = 2 × 150 = 300 cm² = 0.030 m²; 20 kPa = 20 000 Pa
F: p = F / A
I: 20 000 = F ÷ 0.030
F: F = 20 000 × 0.030
A: 600 N
Q7 (F/H) A chef pushes down on a knife with a force of 20 N. The pressure under the blade edge is 400 kPa. Calculate the area of the blade edge in cm².
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Convert first: 400 kPa = 400 000 Pa
F: p = F / A
I: 400 000 = 20 ÷ A
F: A = 20 ÷ 400 000 = 0.000 05 m²
A: 0.000 05 × 10 000 = 0.5 cm²
Q8 (F/H) A drawing pin needs a pressure of 1.2 × 108 Pa to go into wood. Its point has an area of 1.0 × 10−7 m². Calculate the force needed.
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F: p = F / A
I: 1.2 × 108 = F ÷ 1.0 × 10−7
F: F = 1.2 × 108 × 1.0 × 10−7
A: 12 N
Q9 (H) A 1200 kg car exerts a pressure of 196 kPa on the road. It has 4 tyres. Calculate the contact area of each tyre. (g = 9.8 N/kg)
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Step 1 – weight: W = m g = 1200 × 9.8 = 11 760 N
Step 2 – total area
F: p = F / A
I: 196 000 = 11 760 ÷ A
F: A = 11 760 ÷ 196 000 = 0.06 m²
A: each tyre = 0.06 ÷ 4 = 0.015 m²
Q10 (H) Ice can safely take a pressure of 1.5 × 106 Pa. A 55 kg skater balances on one blade. Calculate the minimum contact area of the blade in cm², to 2 significant figures. (g = 9.8 N/kg)
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Step 1 – weight: W = 55 × 9.8 = 539 N
F: p = F / A
I: 1.5 × 106 = 539 ÷ A
F: A = 539 ÷ 1.5 × 106 = 3.59… × 10−4 m²
A: × 10 000 = 3.59… = 3.6 cm² (2 s.f.)
