Power is defined as the time rate at which work is done or energy is transferred ($P = dW/dt$).

1. SI Unit: The SI unit of power is the watt (W), where $1 \text{ W} = 1 \text{ J s}^{-1}$ .
2. Kilowatt (kW): This is a multiple of the SI unit, where $1 \text{ kW} = 1000 \text{ W}$. It is a valid unit of power.
3. Analysis of other options:

• Kilowatt-hour (kWh): This is a commercial unit of electrical energy, defined as $3.6 \times 10^6 \text{ J}$ . It is often confused with power but represents the total energy consumed.
• Joule (J): This is the SI unit of work and energy .
• Dyne: This is the CGS unit of force (not explicitly defined in the provided text, but distinct from power).