Water weighing 1.5 kg is brought to a boil in a kettle with a power of 2 kW, having an efficiency of 84%. How long will it take to heat up if the initial water temperature is 20 degrees?
Task data: m (water mass) = 1.5 kg; N (kettle power, consumed power) = 2 kW (2 * 103 W); η (kettle efficiency) = 84% (0.84); t0 (initial water temperature) = 20 ºС.
Reference data: t (boiling point of water) = 100 ºС; Sv (specific heat of water) = 4200 J / (kg * K).
The duration of heating the water in the kettle is expressed from the formula: η = An / Az = Sv * m * (t – t0) / (N * t), whence t = Sv * m * (t – t0) / (η * N).
Calculation: t = 4200 * 1.5 * (100 – 20) / (0.84 * 2 * 103) = 300 s (5 min).
One of the components of a person's success in our time is receiving modern high-quality education, mastering the knowledge, skills and abilities necessary for life in society. A person today needs to study almost all his life, mastering everything new and new, acquiring the necessary professional qualities.