These tasks: t (operating time of the used heat engine) = 1 h (in SI t = 3600 s); Np (useful power) = 2 kW (2 * 10 ^ 3 W); η (motor efficiency) = 12% (0.12).
We express the heat obtained by the used heat engine from the formula: η = Np / Ns = Np / (Q / t) = Np * t / Q, whence Q = Np * t / η.
Let’s calculate: Q = 2 * 10 ^ 3 * 3600 / 0.12 = 60 * 10 ^ 6 J = 60 MJ.
Answer: In 1 hour, the used heat engine received 60 MJ of heat.
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