Question 1: A 110-V heating element in an electrical water heater is rated at 20 amperes. Find the charge that passes through the element in 10 seconds.
Question 2: A solid-state device in a hand-calculator display has 3 x 10-2 coulombs of charge pass through it in 10 seconds. Find the current used by the calculator in milliamperes.
Question 3: A supertanker unloads 2.0 x 106 gallons of crude oil at a rate of 800 gal/min. How long does it take to unload the tanker-in hours? (Hint: Start with the equation Qv = VA. Isolate the symbol, mt.- Solve for time [t] in minutes. Convert minutes to hours. Use power-of-ten notation.)
Question 4: The refrigeration unit on a meat-delivery truck is rated at 3 ton/hr (that is. 36.000 Btu/hr). Find the amount. of heat the refrigeration unit will remove if it operates for 3.5 hours during an 8-hr on/ of cycle.
Question 5: A sterilizer heating element used in a. hospital is rated at 850 cal/min. It requires 1.8 x 105 calories of heat to sterilize instruments. Find the amount of time the heating element must operate to meet the steriliz2tion standard.
Question 6: In an electric motor. operating at a constant speed, 3 x 10" coulombs of charge have moved through the motor. The motor is operated at a steady current of 50 amperes during the entire period of time. Find the length of time the motor operated at constant speed.
Question 7: A piece of brass. with specific heat. c = 0.091 cal/g•C°. is cooled from 80°C to 40°C. The heat-flow rate out of the material is 15.16 cal/sec for 20 minutes. (Assume the heat-flow rate is constant.)
a. Find the heat given up by the brass.
b. Find the mass of the piece of brass.
Question 8: An air motor used to operate a stirrer that blends chemical dyes uses air at a rate of 168 kg/hr. Find the air mass consumed (used) by the air motor in 5 minutes of operation. (Hint: Isolate "m" in the equation Qm A. Convert 5 minutes to hours. Then substitute numbers in the rearranged equation with "m" isolated and solve for "m" in kg.)
Question 9: For health reasons, air-conditioning is designed to circulate or exchange air in a room every 6 to 10 minutes. An air conditioner with a mass-flow rate of 14.6 kg/min circulates the air in a classroom of size 6mx6mx 2.5 m (about 20 ft x 20 ft x 8 ft). The
room holds 116.8 kg of air. Dry air at 20°C (68°F) has a mass of 1.2 kg per m3. Find: Does this air conditioner meet the design requirement to exchange the mass of air in the room every 6 to 10 minutes? (Hint: Isolate "t" in the fluid rate equation. Qm = m/t. Then solve for t.)
Question 10: While helping build a new home. the heating and air- conditioning technician decided to install a solar-powered heating system that uses a heat-storage tank. Space available for the tank is limited to one cubic meter (1 m3). The tank will hold 1000 kg, of water (which has a specific heat c = 1.0 kcal/kg•C) or 2400 kg of crushed stone (which has a specific heat c = 0.192 kcal/kg-C°). The temperature of either substance is to be raised 40 C°.
a. Find the amount of heat that can be stored in each substance with a 40-Co temperature rise.
b. Find which substance the technician should use if all other conditions are equal.