Watt is unit of power (J/s). Kilowatt-hour is energy (power × time). Joule is SI unit of energy. Electron volt is energy unit (1.6×10⁻¹⁹ J). Remember: power = energy/time. So watt is not energy.
Explanation:
The principle of homogeneity states that you can only add or subtract physical quantities that have the exact same dimensional formula (you can't add mass to length). Therefore, in the equation A = B + C, the terms B and C must have the same dimensions, and their sum will yield a quantity A that also shares those exact same dimensions.
An engine pumps water continuously through a hose. Water leaves the hose with a velocity 'v' and mass per unit length is 'm'. What is the power imparted to the water?
Explanation:
Power is the rate of doing work or imparting kinetic energy (dK/dt). Mass exiting per second = m * v (mass/length * length/time). Kinetic energy imparted per second = 1/2 * (mass per second) * v^2 = 1/2 * (mv) * v^2 = 1/2 * m * v^3. This is a very common advanced mechanics question.
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