Identify which physical quantity uses the unit kg/m^3 in the S.I. system.
Civil Engineering
SI Units
Difficulty: Easy
Choose an option
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AForce
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BDensity
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CVolume
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DPressure
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ESpecific weight
Answer
Correct Answer: Density
Explanation
Introduction / Context:Recognizing units at a glance helps prevent dimensional mistakes in calculations. The unit kg/m^3 appears across materials, soils, fluids, and gases, making it one of the most frequently encountered units in mechanics and civil engineering.
Given Data / Assumptions:
- Density is mass per unit volume.
- kg is the S.I. base unit of mass; m^3 is the S.I. unit of volume.
- Other listed quantities have different S.I. units.
Concept / Approach:Match each physical quantity with its canonical S.I. unit: force → newton (N), volume → m^3, pressure → pascal (N/m^2), specific weight → N/m^3. Only density correctly matches kg/m^3.
Step-by-Step Solution:
Recall definition: density = mass / volume.Substitute S.I. units: mass → kg; volume → m^3 → density unit = kg/m^3.Check alternatives and eliminate mismatches.Verification / Alternative check:
Use known values: water ≈ 1000 kg/m^3; concrete ≈ 2400 kg/m^3; air ≈ 1.2 kg/m^3.Why Other Options Are Wrong:
Force: N; Volume: m^3; Pressure: N/m^2; Specific weight: N/m^3.Common Pitfalls:
Confusing specific weight (weight per volume) with density (mass per volume).Misreading kg/m^3 as m^3/kg (specific volume).Final Answer:
Density