Physics: What is the change in internal energy of a system

Physics: What is the change in internal energy of a system

Subject: Physics    / General Physics
Question

1. What is the change in internal energy of a system that takes in 3.40 ? 106 J of heat, and does 4.50 ? 105 J of work while dissipating 6.00 ? 106 J of heat? _________J
2. Steam locomotives have an efficiency of 17.0% and operate with a hot steam temperature of 375°C.
a. What would the cold reservoir temperature be if this were a Carnot engine? 265 Celcius
b. What would the maximum efficiency of this steam engine be if its cold reservoir temperature were 150°C? ________%

3.

(a) What is the best coefficient of performance for a heat pump that has a hot reservoir temperature of 52.0°C and a cold reservoir temperature of -20.0°C? ______ (b) How much heat in kilocalories would it pump into the warm environment if 3.60 ? 107 J of work (10.0 kW·h) is put into it?________ kcal(c) Assume the cost of this work input is 10¢/kW·h. Also assume that the cost of direct production of heat by burning natural gas is 85.0¢ per therm (a common unit of energy for natural gas), where a therm equals 1.055 ? 108 J. Compare the cost of producing the same amount of heat by each method. ___________(cost of heat pump / cost of natural gas)
4.
(a) How much heat flows from 1.00 kg of water at 46.0°C when it is placed in contact with 1.00 kg of 18°C water in reaching equilibrium?__________ J

5. (a) What is the intensity in W/m2 of a laser beam used to burn away cancerous tissue that, when 90.0% absorbed, puts 500 J of energy into a circular spot 3.00 mm in diameter in 4.00 s? _______W/m^2

(b) Compare this intensity to the average intensity of sunlight (about 1 kW/m2).
(intensity of laser / avg intensity of sunlight) = ___________