Units — work in the SI system: Select the correct SI unit of work (and energy) used in physics and engineering.

Introduction / Context:
Clear unit identification prevents calculation errors and ensures proper interpretation of results. In SI, work and energy share the same unit, important for thermodynamics, mechanics, and electrical systems (via watt·second).

Given Data / Assumptions:

• Standard SI (International System of Units).
• Work W = force * displacement in the direction of force.

Concept / Approach:
In SI, the unit of force is newton (N) and distance is meter (m). Therefore, work has unit N·m, which is defined as the joule (J).

Step-by-Step Solution:
Work W = F * s.Units: N * m = N·m = joule (J).Hence the correct SI unit is the joule.

Verification / Alternative check:
1 joule = 1 newton-meter = 1 kg·m^2/s^2. This is consistent with kinetic energy 0.5mv^2 and potential energy mgh.

Why Other Options Are Wrong:

• newton: Unit of force, not work.
• erg: CGS unit of work (1 erg = 1e−7 J).
• kg-m: Not an SI unit for work; dimensions do not match energy.

Common Pitfalls:

• Using N·m as torque; while the unit matches joule dimensionally, torque is not energy. Context distinguishes them.

Final Answer:
joule