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.
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AWork
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BTorque
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CEnergy
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DAll the above.
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EOnly 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.