Example 1 · level 1
A block has a mass of 89 kg and a volume of 0.01 m³. Find its density in kg/m³.
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- ρ = 89 ÷ 0.01 = 8900 kg/m³.
Answer: 8,900
CLASS 9 SCIENCE · GRAVITATION (FLUIDS)
Density, relative density and pressure
Density = mass ÷ volume (kg/m³). Relative density = density ÷ density of water (1000 kg/m³). Pressure = thrust ÷ area (Pa = N/m²).
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Worked examples
Example 2 · level 2
A wooden almirah weighing 1,050 N stands on a floor; the total area of its base in contact with the floor is 0.25 m². Find the pressure it exerts (in Pa).
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- P = 1,050 ÷ 0.25 = 4,200 Pa.
Answer: 4,200 Pa
Example 3 · level 3
The density of a piece of iron is 7800 kg/m³. Find its relative density (density of water = 1000 kg/m³). Will it float or sink in water? (Enter the relative density.)
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- RD = 7800 ÷ 1000 = 7.8.
- RD > 1, so it sinks in water.
Answer: 7.8