Section 3 - Heat engines
3.1 During a cycle, a heat engine receives 2.78×10^4 J of heat from the hot reservoir and gives up 1.83×10^4 J of heat to the cold
reservoir. (a) What is the net work performed during one cycle? Make sure to include the correct sign. (b) Is work done on the
system, or does the system do work on its suroundings?
(a) J
(b) i. Work is done on the system
ii. Work is done by the system
3.2 A heat engine does 2.4×10^5 J of work during each cycle. If the engine loses 1.8×10^5 J of heat to the cold reservoir in each
cycle, how much heat is transferred from the hot reservoir during the cycle?
J
3.3 A mountain climber gains 897 m in elevation on a particular hike. Consider the climber's body as a heat engine, with heat for
work provided by burning food (the "hot reservoir") and excess heat radiated into the mountain air (the "cold reservoir"). (a) If
her mass is 62.3 kg, how much work does she do changing her gravitational potential energy? (b) If she radiates 1.67×10^5 J
of heat during the climb, and her internal energy doesn't change, how much heat does the food supply?
(a) J
(b) J
3.4 The horsepower rating commonly used for engines indicates the rate at which they can do work. A one-horsepower engine
can do 746 J of work each second. A lawn mower has a 6.50 horsepower engine that runs at 3800 rpm. Each revolution of
the engine represents one engine cycle. (a) What amount of work does the engine do on each cycle? (b) If the hot reservoir of
the engine supplies 142 J of heat each cycle, hot much heat must the engine expel to the cold reservoir?
(a) J
(b) J(^382) Copyright 2007 Kinetic Books Co. Chapter 20 Problems