Pressure and thrust: Class 9 practice
Pressure is thrust (force perpendicular to a surface) divided by the area it acts on: P = F/A, measured in pascals (1 Pa = 1 N/m²). Read the method, follow the three worked examples, then try the six questions.
What you should know first
- Area units
- Weight = mg
The idea behind pressure and thrust
Pressure is thrust (force perpendicular to a surface) divided by the area it acts on: P = F/A, measured in pascals (1 Pa = 1 N/m²). Smaller area → bigger pressure.
Step-by-step method
- Convert area to m² (1 cm² = 10⁻⁴ m²).
- Weight as thrust: F = mg.
- P = F ÷ A.
Worked example 1 (Basic)
A thrust of 450 N acts on an area of 0.5 m². Find the pressure.
- P = 450 ÷ 0.5
- P = 900 Pa
- Answer: 900 Pa
Worked example 2 (Standard)
A 70 kg block rests on a face of area 40 cm². Taking g = 10 m/s², find the pressure it exerts.
- Thrust = mg = 700 N
- A = 40 cm² = 0.004 m²
- P = 700 ÷ 0.004 = 175000 Pa
- Answer: 175000 Pa
Worked example 3 (Challenge)
What area is needed so that a 250 N weight exerts only 3000 Pa?
- A = F ÷ P = 250 ÷ 3000
- A = 0.083 m²
- Answer: 0.083 m²
Common mistakes and misconceptions
- Leaving area in cm²
- Using mass instead of weight
Practice questions
- (Basic) A thrust of 330 N acts on an area of 2 m². Find the pressure.
- (Basic) A thrust of 330 N acts on an area of 4 m². Find the pressure.
- (Standard) A 65 kg block rests on a face of area 40 cm². Taking g = 10 m/s², find the pressure it exerts.
- (Standard) A 30 kg block rests on a face of area 50 cm². Taking g = 10 m/s², find the pressure it exerts.
- (Challenge) What area is needed so that a 100 N weight exerts only 6000 Pa?
- (Challenge) What area is needed so that a 1000 N weight exerts only 5000 Pa?
Answer key with full working
- Q1: P = 330 ÷ 2 → P = 165 Pa → Answer: 165 Pa
- Q2: P = 330 ÷ 4 → P = 82.5 Pa → Answer: 82.5 Pa
- Q3: Thrust = mg = 650 N → A = 40 cm² = 0.004 m² → P = 650 ÷ 0.004 = 162500 Pa → Answer: 162500 Pa
- Q4: Thrust = mg = 300 N → A = 50 cm² = 0.005 m² → P = 300 ÷ 0.005 = 60000 Pa → Answer: 60000 Pa
- Q5: A = F ÷ P = 100 ÷ 6000 → A = 0.017 m² → Answer: 0.017 m²
- Q6: A = F ÷ P = 1000 ÷ 5000 → A = 0.200 m² → Answer: 0.200 m²
Syllabus note
This skill is listed under "Gravitation" for Class 9 in the NCERT/CBSE books. ICSE, IGCSE, IB and state boards may teach it in a different chapter or year.
Answers on this page are generated and automatically re-checked by a second, independent calculation. They have not been reviewed by a teacher — if you spot a problem, tell us on WhatsApp.
Related practice and notes
Frequently asked questions
Which chapter is pressure and thrust in?
"Gravitation", Class 9 Physics (NCERT/CBSE). Other boards may place it differently.
How were the answers checked?
Answers on this page are generated and automatically re-checked by a second, independent calculation. They have not been reviewed by a teacher — if you spot a problem, tell us on WhatsApp.