College Physics
1st Edition
ISBN: 9781938168000
Author: Paul Peter Urone, Roger Hinrichs
Publisher: OpenStax College
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Textbook Question
Chapter 7, Problem 26CQ
If the efficiency of a coal-fired electrical generating plant is 35%, then what do we mean when we say that energy is a conserved quantity?
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Chapter 7 Solutions
College Physics
Ch. 7 - Give an example of something think of as work in...Ch. 7 - Give an example of a situation in which there is a...Ch. 7 - Describe a situation in which a force is exerted...Ch. 7 - The person in Figure 7.33 does work on the lawn...Ch. 7 - Work done on a system puts energy into it Work...Ch. 7 - When solving for speed in Example 7.4, we kept...Ch. 7 - In Example 7.7, we calculated the final speed of a...Ch. 7 - Does the work you do on a book when you lift it...Ch. 7 - What is a conservative force?Ch. 7 - The force exerted by a diving board is...
Ch. 7 - Define mechanical energy. What is the relationship...Ch. 7 - What is the relationship of potential energy to...Ch. 7 - Consider the following scenario. A car for which...Ch. 7 - Describe the energy transfers and transformations...Ch. 7 - Do devices with efficiencies of less than one...Ch. 7 - List four different forms or types of energy. Give...Ch. 7 - List the energy conversions that occur when riding...Ch. 7 - Most electrical appliances are rated in watts....Ch. 7 - Explain, in terms of the definition of power, why...Ch. 7 - A spark of static electricity, such as that you...Ch. 7 - Explain why it is easier to climb a mountain on a...Ch. 7 - Do you do work on the outside world when you rub...Ch. 7 - Shivering is an involuntary response to lowered...Ch. 7 - Discuss the relative effectiveness of dieting and...Ch. 7 - What is the difference between energy conservation...Ch. 7 - If the efficiency of a coal-fired electrical...Ch. 7 - How much work does a supermarket checkout...Ch. 7 - A 75.0-kg person climbs stairs, gaining 2.50...Ch. 7 - (a) Calculate the work done on a 1500-kg elevator...Ch. 7 - Suppose a car travels 108 km at a speed of 30.0...Ch. 7 - Calculate the work done by an 85.0-kg man who...Ch. 7 - How much work is done by the boy pulling his...Ch. 7 - A shopper pushes a grocery cart 20.0 m at constant...Ch. 7 - Suppose the ski patrol lowers a rescue sled and...Ch. 7 - Compare the kinetic energy of a 20,000-kg truck...Ch. 7 - (a) How fast must a 3000-kg elephant move to have...Ch. 7 - Confirm the value given for the kinetic energy of...Ch. 7 - (a) Calculate the force needed to bring a 950-kg...Ch. 7 - A car's bumper is designed to withstand a 4.0-km/h...Ch. 7 - Boxing gloves are padded to lessen the force of a...Ch. 7 - Using energy considerations, calculate the average...Ch. 7 - A hydroelectric power facility (see Figure 7.38)...Ch. 7 - (a) How much gravitational potential energy...Ch. 7 - Suppose a 350-g kookaburra (a large kingfisher...Ch. 7 - In Example 7.7, we found that the speed of a...Ch. 7 - A 100-g toy car is propelled by a compressed...Ch. 7 - In a downhill ski race, surprisingly, little...Ch. 7 - A 5.00105 -kg subway train is brought to a stop...Ch. 7 - A pogo stick has a spring with a force constant of...Ch. 7 - A 60.0-kg skier with an initial speed of 12.0 m/s...Ch. 7 - (a) How high a hill can a car coast up (engine...Ch. 7 - Using values from Table 7.1, how many DNA...Ch. 7 - Using energy considerations and assuming...Ch. 7 - If the energy in fusion bombs were used to supply...Ch. 7 - (a) Use of hydrogen fusion to supply energy is a...Ch. 7 - The Crab Nebula (see Figure 7.41) pulsar is the...Ch. 7 - Suppose a star 1000 times brighter than our Sun...Ch. 7 - A person in good physical condition can put out...Ch. 7 - What is the cost of operating a 3.00-W electric...Ch. 7 - A large household air conditioner may consume 15.0...Ch. 7 - (a) What is the average power consumption in watts...Ch. 7 - (a) What is the average useful power output of a...Ch. 7 - A 500-kg dragster accelerates from rest to a final...Ch. 7 - (a) How long will it take an 850-kg car with a...Ch. 7 - (a) Find the useful power output of an elevator...Ch. 7 - (a) What is the available energy content, in...Ch. 7 - (a) How long would it takea 1.50105 -kg airplane...Ch. 7 - Calculate the power output needed for a 950-kg car...Ch. 7 - (a) Calculate the power per square meter reaching...Ch. 7 - (a) How long can you rapidly climb stairs...Ch. 7 - (a) What is the power output in watts and...Ch. 7 - Calculate the power output in watts and horsepower...Ch. 7 - (a) What is the efficiency of an out-of-condition...Ch. 7 - Energy that is not utilized for work or heat...Ch. 7 - Using data from Table 7.5, calculate the daily...Ch. 7 - What is the efficiency of a subject on a treadmill...Ch. 7 - Shoveling snow can be extremely taxing because the...Ch. 7 - Very large forces are produced in joints when a...Ch. 7 - Jogging on hard surfaces with insufficiently...Ch. 7 - (a) Calculate the energy in kJ used by a 55.0-kg...Ch. 7 - Kanellos Kanellopoulos flew 119 km from Crete to...Ch. 7 - The swimmer shown in Figure 7.44 exerts an average...Ch. 7 - Mountain climbers carry bottled oxygen when at...Ch. 7 - The awe-inspiring Great Pyramid of Cheops was...Ch. 7 - (a) How long can you play tennis on the 800 kJ...Ch. 7 - Integrated Concepts (a) Calculate the force the...Ch. 7 - Integrated Concepts A 75.0-kg cross-country skier...Ch. 7 - Integrated Concepts The 70.0-kg swimmer in Figure...Ch. 7 - Integrated Concepts A toy gun uses a spring with a...Ch. 7 - Integrated Concepts (a) What force must be...Ch. 7 - Unreasonable Results A car advertisement claims...Ch. 7 - Unreasonable Results Body fat is metabolized,...Ch. 7 - Construct Your Own Problem Consider a person...Ch. 7 - Construct Your Own Problem Consider humans...Ch. 7 - Integrated Concepts A 105-kg basketball player...
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- What do we pay the electric company for, power or energy? In what units?arrow_forwardWhat is the difference in the operations of a 2-hp motor and a 1-hp motor?arrow_forwardA large household air conditioner may consume 15.0 kW of power. What Is the cost of operating this air conditioner 3.00 h per day for 30.0 d if the cost of electricity is $0.110 per kWh ?arrow_forward
- Energy is conventionally measured in Calories as well as in joules. One Calorie in nutrition is 1 kilocalorie, which we define in Chapter 11 as 1 kcal = 4 186 J. Metabolizing 1 gram of fat can release 9.00 kcal. A student decides to try to lose weight by exercising. She plans to run up and down the stairs in a football stadium as fast as she can and as many times as necessary. Is this in itself a practical way to lose weight? To evaluate the program, suppose she runs up a flight of 80 steps, each 0.150 m high, in 65.0 s. For simplicity, ignore the energy she uses in coming down (which is small). Assume that a typical efficiency for human muscles is 20.0%. This means that when your body converts 100 J from metabolizing fat, 20 J goes into doing mechanical work (here, climbing stairs). The remainder goes into internal energy. Assume the students mass is 50.0 kg. (a) How many times must she run the flight of stairs to lose 1 pound of fat? (b) What is her average power output, in watts and in horsepower, as she is running up the stairs?arrow_forwardExplain, in terms of the definition of power, why energy consumption is sometimes listed in kilowatt-hours rather than joules. What is the relationship between these two energy units?arrow_forwardA typical automobile engine has an efficiency of 25 . Suppose that the engine of a 1000-kg automobile has a maximum power output of 140 hp. What is the maximum grade that the automobile can climb at 50 km/h if the frictional retarding force on it is 300 N?arrow_forward
- Water falls over a dam of height h with a mass flow rate of R, in units of kilograms per second. (a) Show that the power available from the water is P=Rgh where g is the free-fall acceleration. (b) Each hydroelectric unit at the Grand Coulee Dam takes in water at a rate of 8.50 105 kg/s from a height of 87.0 m. The power developed by the falling water is converted to electric power with an efficiency of 85.0%. How much electric power does each hydroelectric unit produce?arrow_forwardThe man of the preceding problem consumes approximately 1.05107J (2500 food calories) of energy per day in maintaining a constant weight. What is the average power he produces over a day? Compare this with his power production when he runs up the stairs.arrow_forwardWhat is the efficiency of a subject on a treadmill who puts out work at the rate of 100 W while consuming oxygen at the rate of 2.00 L/min? (Hint: See Table 7.5.)arrow_forward
- What is the cost of operating a 3.00-W electric clock for a year if the cost of electricity is 0.0900 per kWh ?arrow_forwardA person drops a pebble of mass m1from a height h, and it hits the floor with kinetic energy K. The person drops another pebble of mass m2, from a height of 2h , and it hits the floor with the same kinetic energy K. How do the masses of the pebbles compare?arrow_forwardDistinguish between what a physicist and a politician might each mean when using the term energy conservation.arrow_forward
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