20A

please circle the answers please circle the answers please circle the answers please circle the answers please circle the answers please circle the answers please circle the answers please circle the answers please circle the answers please circle the answers

1. [-/1 Points] DETAILS WAUNIPHYSAV1 20.P.001. MY NOTES ASK YOUR TEACHER PRACTICE ANOTHER Suppose a woman does 413 j of work and dissipates 7454 J of heat in the process. (a) What is the change in her internal energy in kilocalories, assuming no change in temperature or consumption of food? (That is, there is no other energy transfer.) kcal (b) What is her efficiency? % 2. [-/1 Points] DETAILS WAUNIPHYSAV1 20.P.003. MY NOTES ASK YOUR TEACHER PRACTICE ANOTHER A certain heat engine does 12.2 kj of work and dissipates 9.34 kj of waste heat in a cyclical process. (a) What was the heat input to this engine? KJ (b) What was its efficiency? % 3. [-/1 Points] DETAILS WAUNIPHYSAV1 20.P.005. MY NOTES ASK YOUR TEACHER PRACTICE ANOTHER Assume that the turbines at a coal-powered power plant were upgraded resulting in an improvement in efficiency of 5.74%. Assume that prior to the upgrade the power station had an efficiency of 43%, and that the heat transfer into the engine in one day is still the same at 2.13 x 1014 J. (a) How much more electrical power is produced due to the upgrade? KW (b) How much less heat transfer occurs to the environment due to the upgrade? J4. [-/1 Points] DETAILS WAUNIPHYSAV1 20.P.008. MY NOTES ASK YOUR TEACHER PRACTICE ANOTHER A 500 kg dragster reaches a speed of 133 m/s on level ground, starting from rest. Its efficiency is only 7.40% in producing kinetic energy, because of friction and its design for high power without regard to efficiency. (a) How many gallons of fuel does it use during this acceleration, given there are 1.30 x 108 j of energy per gallon? gal (b) How much waste heat is produced? 5. [-/1 Points] DETAILS WAUNIPHYSAV1 20.P.013.TUTORIAL. MY NOTES ASK YOUR TEACHER PRACTICE ANOTHER A fairly efficient steam turbine engine fired by coal is used to drive an electric generator. The generator operates between 2100 C and 385.C. (a) Determine the maximum possible efficiency of the engine. % (b) The engine absorbs 1.05 x 105 J from the hot reservoir every second. If the actual efficiency of the engine is 47.3%, determine the mechanical power the engine delivers. KW 12 Tutorial 6. [-/1 Points] DETAILS WAUNIPHYSAV1 20.P.014. MY NOTES ASK YOUR TEACHER PRACTICE ANOTHER What is the coefficient of performance of an ideal heat pump that pumps heat from a cold temperature of -19.9C to a hot temperature of 35.0.C?7. [-/1 Points] DETAILS WAUNIPHYSAV1 20.P.015. MY NOTES ASK YOUR TEACHER PRACTICE ANOTHER (a) What is the best coefficient of performance for a heat pump that has a hot reservoir temperature of 59.3C and a cold reservoir temperature of -12.2.C? (b) How much heat in kilocalories would it pump into the warm environment if 3.60 x 10/J of work (10.0 kW . h) is put into it? kcal (c) Assume the cost of this work input is 10c/KW . h. Also assume that the cost of direct production of heat by burning natural gas is 89.0c per therm (a common unit of energy for natural gas), where a therm equals 1.055 x 108 J. Compare the cost of producing the same amount of heat by each method. cost of heat pump = cost of natural gas 8. [-/1 Points] DETAILS WAUNIPHYSAV1 20.P.016. MY NOTES ASK YOUR TEACHER PRACTICE ANOTHER Suppose you want to operate an ideal refrigerator with a cold temperature of -18.8 C, and you would like it to have a coefficient of performance of 7.70. What is the hot reservoir temperature for such a refrigerator? OC 9. [-/1 Points] DETAILS WAUNIPHYSAV1 20.P.012.TUTORIAL. MY NOTES ASK YOUR TEACHER PRACTICE ANOTHER The ice maker inside a refrigerator makes ice cubes at 0.0C from water that is at 16.7C when it first enters the ice maker. If this machine is rated at 294 W and has a 3.86 coefficient of performance, what is the maximum amount of ice it can produce in a 24 hour period without any interruption or stoppage? Assume that the ice maker works just like a refrigerator. The specific heat of water is 4184 J/(kg . .C), and the latent heat of fusion of ice is 33.4 x 104 J/kg. kg 123 Tutorial10. [-/1 Points] DETAILS WAUNIPHYSAV1 20.P.020. MY NOTES ASK YOUR TEACHER PRACTICE ANOTHER Practical steam engines utilize 507C steam, which is later exhausted at 204.C. (a) What is the maximum efficiency that such a heat engine can have? % (b) Since 204C steam is still quite hot, a second steam engine is sometimes operated using the exhaust of the first. What is the maximum efficiency of the second engine if its exhaust has a temperature of 150C? % (c) What is the overall efficiency of the two engines? %