SI units — energy Which one of the following is the SI unit of energy?

Introduction / Context:
Correct use of SI units is essential in engineering calculations. Energy, work, and power are distinct quantities with different units and dimensions.

Given Data / Assumptions:

• Standard SI base and derived units are used.
• Energy and work are dimensionally equivalent.

Concept / Approach:
The SI unit of energy (and work) is the joule (J). One joule equals one newton·meter: 1 J = 1 N·m = 1 kg·m^2/s^2. Power is the time rate of doing work, measured in watts (W), where 1 W = 1 J/s. Forces in SI are measured in newtons (N); dyne is a cgs unit of force, not energy.

Step-by-Step Solution:

Verification / Alternative check:
Dimensional analysis: energy has dimension M L^2 T^−2; joule matches this, while watt has M L^2 T^−3.

Why Other Options Are Wrong:

• Dyne: cgs unit of force.
• Watt: SI unit of power, not energy.
• kg·m: Not a correct SI energy unit; missing time dimension.
• newton·meter-second: Has wrong time exponent; not energy.

Common Pitfalls:
Confusing joule and watt; forgetting that energy and work share the same unit.

Final Answer:
joule