One of the most efficient engines built so far has thefollowing characteristics:

Question

One of the most efficient engines built so far has thefollowing characteristics: combustion chamber temperature = 1900 C,exhaust temperature = 430 C, 7.0 * 10^9 cal of fuel produces 1.4 *10^10 J of work in one hour. What is the power output, in hp, ofthis engine? A) 8.3 kW B) 5.2 kW C) 6.1 kW D) 7.4 kW I know how to calculate the efficiency, e = 68%, but I'm lostfrom there. Thanks! One of the most efficient engines built so far has thefollowing characteristics: combustion chamber temperature = 1900 C,exhaust temperature = 430 C, 7.0 * 10^9 cal of fuel produces 1.4 *10^10 J of work in one hour. What is the power output, in hp, ofthis engine? A) 8.3 kW B) 5.2 kW C) 6.1 kW D) 7.4 kW I know how to calculate the efficiency, e = 68%, but I'm lostfrom there. Thanks!

Explanation / Answer

Work output W =1.4x1010 J in 1 hour Power output P = 1.4x1010 J/1 hour =1.4x1010 J /3600 s                        = 3.89x106 W = 3.89 MW = 3890 kW                        = 3890 kW/0.750kW/HP                         =5187 HP = 5.2 kHP I think they have ixed up units in the answers given. The qn asks for answer in HP.

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