In S.I. terminology, the joule (J) equals newton–metre (Nm). Identify the physical quantities for which these units are used in practice, noting the conventional use for torque as well.

Civil Engineering SI Units Difficulty: Easy
Choose an option
  • A
    Work
  • B
    Torque
  • C
    Energy
  • D
    All the above.
  • E
    Only work and energy

Answer

Correct Answer: All the above.

Explanation

Introduction / Context:In S.I., work and energy share the unit joule (J). Since 1 J = 1 Nm, the same dimensional product appears in torque calculations. However, conventionally engineers write torque in Nm (not J) to distinguish the vectorial, moment-like nature of torque from scalar energy or work, even though the dimensions match.

Given Data / Assumptions:

  • Work and energy are scalars measured in joules.
  • Torque (moment of force) is a vector (or axial vector) commonly expressed as Nm.
  • 1 J = 1 Nm in S.I. dimensional terms.

Concept / Approach:

Use the work definition W = F * s (component along displacement) and torque definition M = F * d (perpendicular distance). Both are force times distance, but they represent different physical concepts. Hence, the shared unit does not imply identical physical meaning.

Step-by-Step Solution:

Write work: W = F * s → unit Nm → called J in S.I.Write energy: Energy measured in J by definition (work-capacity equivalence).Write torque: M = F * d → unit Nm, conventionally not denoted as J to avoid confusion.Therefore, the units apply across work, energy, and torque, with naming conventions distinguishing torque.

Verification / Alternative check:

Dimensional analysis: N = kgm/s^2, so Nm = kgm^2/s^2. This dimension appears in both torque and energy computations, confirming the equivalence of units despite different physical interpretations.

Why Other Options Are Wrong:

  • Only work and energy: Excludes torque, which also uses Nm in practice.

Common Pitfalls:

  • Interchanging 'joule' with torque values in reports; best practice labels torque explicitly as Nm.
  • Forgetting that torque’s direction depends on the right-hand rule, unlike scalar energy.

Final Answer:

All the above.

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