SAT Subject Physics Practice Question 219: Answer and Explanation
65. During each cycle, a heat engine with an efficiency of 25% takes in 800 J of energy. How much waste heat is expelled during each cycle?
A. 100 J
B. 200 J
C. 300 J
D. 400 J
E. 600 J
Correct Answer: E
If the efficiency of the engine is 25%, then the energy that is output for useful work is 25% of the input energy, which is (25%)(800 J) = 200 J. The remaining 800 J – 200 J = 600 J is expelled as waste heat.