Force and Pressure Solved Examples (Class 8 Science)
Force and pressure numericals help students understand how force distributed over area affects pressure. These problems train calculation of pressure, forc
TL;DR: Force and pressure numericals help students understand how force distributed over area affects pressure. These problems train calculation of pressure,…
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Force and pressure numericals help students understand how force distributed over area affects pressure. These problems train calculation of pressure, forc
Force and Pressure — Solved Numerical Examples (Step by Step)
Example 1: A box of mass 50 kg rests on a floor with a contact area of 2 m². Calculate the pressure exerted by the box on the floor. (g = 10 m/s²)
Solution: Mass of box = 50 kg, g = 10 m/s², Area = 2 m². Force = mass × g = 50 × 10 = 500 N. Pressure = Force / Area = 500 / 2 = 250 Pa.
Example 2: A needle has a tip area of 0.01 mm² and a force of 50 N is applied. Calculate the pressure at the needle tip.
Solution: Force = 50 N, Area = 0.01 mm² = 0.01 × 10^-6 m² = 1 × 10^-8 m². Pressure = Force / Area = 50 / (1 × 10^-8) = 5 × 10^9 Pa.
Example 3: A person weighing 600 N stands on one foot with contact area 0.05 m². Find the pressure on the ground.
Solution: Force (weight) = 600 N, Area = 0.05 m². Pressure = Force / Area = 600 / 0.05 = 12000 Pa = 12 kPa.
Example 4: A water tank with base area 3 m² is filled with water to a height of 2 m. Calculate the pressure at the bottom. (Density of water = 1000 kg/m³, g = 10 m/s²)
Solution: Height = 2 m, Density = 1000 kg/m³, g = 10 m/s². Pressure = Density × g × height = 1000 × 10 × 2 = 20,000 Pa.
Example 5: A brick of mass 2 kg is placed on a surface with dimensions 20 cm × 10 cm. Calculate the pressure exerted. (g = 10 m/s²)
Solution: Mass = 2 kg, g = 10 m/s², Force = 2 × 10 = 20 N. Area = 20 cm × 10 cm = 0.2 m × 0.1 m = 0.02 m². Pressure = 20 / 0.02 = 1000 Pa.
Example 6: A 70 kg person sits on a chair. The chair has 4 legs, each with contact area 0.01 m². Calculate total pressure. (g = 10 m/s²)
Solution: Weight = 70 × 10 = 700 N. Total contact area = 4 × 0.01 = 0.04 m². Pressure = 700 / 0.04 = 17,500 Pa.
Tips
- Remember: Pressure = Force / Area. Force is often weight (mass × g).
- Convert all units to SI before calculating: cm² to m², mm² to m².
- Smaller contact area means higher pressure for the same force.
Frequently Asked Questions
Why does a needle pierce cloth easily while a blunt stick does not?
A needle has a very small tip area, so the same force creates enormous pressure, allowing it to pierce. A blunt stick has larger area, spreading force over more space, creating less pressure.
What is the difference between force and pressure?
Force is the total push or pull (measured in Newtons). Pressure is how concentrated that force is over an area (Force per unit area, measured in Pascals).
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