Difficulty: Easy
Correct Answer: Newton
Explanation:
Introduction / Context:Force is one of the most fundamental quantities in mechanics. In the S.I. (International System of Units), consistent unit selection is crucial so that equations like F = m * a remain dimensionally correct and easy to apply across engineering problems ranging from structural analysis to fluid mechanics and machine design.
Given Data / Assumptions:
Concept / Approach:From Newton’s second law, force must carry units kg * m/s^2. The S.I. assigns a special name to this derived unit: the newton (symbol N). One newton is the force required to accelerate a mass of 1 kg at 1 m/s^2. Distinguishing force (newton) from energy (joule) and mass (kilogram) prevents common dimensional mistakes in calculations and design checks.
Step-by-Step Solution:
Write the governing relation: F = m * a.Insert S.I. units: m → kg; a → m/s^2; therefore F units → kg * m/s^2.Recognize that kg * m/s^2 is named “newton” (N) in the S.I. system.Verification / Alternative check:
Check dimensional homogeneity in common formulas (e.g., work W = F * s has units N * m = joule), confirming that newton is a force unit distinct from joule (energy).Why Other Options Are Wrong:
Kilograms: unit of mass, not force.Joule: unit of energy/work (N * m), not force.Erg: cgs unit of energy (1 erg = 10^-7 J), not S.I. force.Watt: unit of power (J/s), not force.Common Pitfalls:
Confusing kilograms-force (kgf) with kilogram (mass) or with newton; in S.I., force should be expressed in newtons.Using energy units (J) when a force value (N) is required.Final Answer:
Newton
Discussion & Comments