Work–energy in SI units — meaning of one joule: Choose the statement that correctly defines one joule in the SI system.

Introduction / Context:Clarity on SI definitions avoids unit-conversion errors in energy, power, and torque problems. The joule (J) is the standard unit of work and energy in the International System of Units.

Given Data / Assumptions:

• Work W = F * s when force and displacement are collinear.
• SI base units: newton (N) for force, meter (m) for length.

Concept / Approach:By definition, 1 joule equals the work done by a 1 newton force acting through 1 meter in the direction of the force. Hence, 1 J = 1 N·m. Non-SI definitions (dyne–cm) correspond to the CGS unit called the erg (1 erg = 1 dyne·cm = 1e−7 J).

Step-by-Step Solution:Select the statement matching W = F * s with F = 1 N and s = 1 m.Compute W = 1 * 1 = 1 N·m = 1 J.Therefore, the correct choice is the SI definition with 1 N and 1 m.

Verification / Alternative check:Dimensional check: J = kg·m^2/s^2. Since N = kg·m/s^2, multiplying by m yields kg·m^2/s^2, confirming consistency.

Why Other Options Are Wrong:

• 1 kg and 1 g refer to mass, not force; SI force is the newton.
• 1 dyne and 1 cm define the CGS unit (erg), not the SI joule.

Common Pitfalls:

• Mixing energy (J) and torque (N·m). They share units but represent different physical quantities; context distinguishes them.

Final Answer:work is done by a force of 1 N when it displaces a body through 1 m