College Physics 1st Edition solutions

College Physics 1
Problem 38PE (a) How long will it take an 850-kg car with a useful power output of 40.0 hp (1 hp = 746 W) to reach a speed of 15.0 m/ s, neglecting friction? (b) How long will this acceleration take if the car also climbs a 3.00-m-high hill in the process?

College Physics 1
Problem 1CQ Give an example of something we think of as work in everyday circumstances that is not work in the scientific sense. Is energy transferred or changed in form in your example? If so, explain how this is accomplished without doing work.

College Physics 1
Problem 1PE How much work does a supermarket checkout attendant do on a can of soup he pushes 0.600 m horizontally with a force of 5.00 N? Express your answer in joules and kilocalories.

College Physics 1
Problem 2CQ Give an example of a situation in which there is a force and a displacement, but the force does no work. Explain why it does no work.

College Physics 1
Problem 2PE A 75.0-kg person climbs stairs, gaining 2.50 meters in height. Find the work done to accomplish this task.

College Physics 1
Problem 3CQ Describe a situation in which a force is exerted for a long time but does no work. Explain.

College Physics 1
Problem 3PE (a) Calculate the work done on a 1500-kg elevator car by its cable to lift it 40.0 m at constant speed, assuming friction averages 100 N. (b) What is the work done on the lift by the gravitational force in this process? (c) What is the total work done on the lift?

College Physics 1
The person in Figure \(7.33\) does work on the lawn mower. Under what conditions would the mower gain energy? Under what conditions would it lose energy? Figure \(7.33\) Equation Transcription: Text Transcription: 7.33

College Physics 1
Suppose a car travels \(108 \mathrm{~km}\) at a speed of \(30.0 \mathrm{~m} / \mathrm{s}\), and uses \(2.0 \text { gal }\) of gasoline. Only \(30 \%\) of the gasoline goes into useful work by the force that keeps the car moving at constant speed despite friction. (See Table \(7.1\) for the energy con

College Physics 1
Problem 5CQ Work done on a system puts energy into it. Work done by a system removes energy from it. Give an example for each statement.

College Physics 1
Calculate the work done by an \(\text { 85.0-kg }\) man who pushes a crate \(4.00 \mathrm{~m}\) up along a ramp that makes an angle of \(20.0^{\circ}\) with the horizontal. (See Figure \(7.35\).) He exerts a force of \(500 N\) on the crate parallel to the ramp and moves at a constant speed. Be certai

College Physics 1
When solving for speed in Example \(7.4\), we kept only the positive root. Why? Equation Transcription: Text Transcription: 7.4

College Physics 1
How much work is done by the boy pulling his sister \(30.0 \mathrm{~m}\) in a wagon as shown in Figure \(7.36\)? Assume no friction acts on the wagon. Figure \(7.36\) The boy does work on the system of the wagon and the child when he pulls them as shown.

College Physics 1
In Example 7.7, we calculated the final speed of a roller coaster that descended 20 m in height and had an initial speed of 5 m/s downhill. Suppose the roller coaster had had an initial speed of 5 m/s uphill instead, and it coasted uphill, stopped, and then rolled back down to a final point 20 m belo

College Physics 1
Problem 7PE A shopper pushes a grocery cart 20.0 m at constant speed on level ground, against a 35.0 N frictional force. He pushes in a direction 25.0 below the horizontal. (a) What is the work done on the cart by friction? (b) What is the work done on the cart by the gravitational force? (c) What

College Physics 1
Problem 8CQ Does the work you do on a book when you lift it onto a shelf depend on the path taken? On the time taken? On the height of the shelf? On the mass of the book?

College Physics 1
Suppose the ski patrol lowers a rescue sled and victim, having a total mass of \(90.0 \mathrm{~kg}\), down a \(60.0^{\circ}\) slope at constant speed, as shown in Figure \(7.37\). The coefficient of friction between the sled and the snow is \(0.100\). (a) How much work is done by friction as the s

College Physics 1
Problem 9CQ What is a conservative force?

College Physics 1
Problem 9PE Compare the kinetic energy of a 20,000-kg truck moving at 110 km/h with that of an 80.0-kg astronaut in orbit moving at 27,500 km/h.

College Physics 1
Problem 10CQ The force exerted by a diving board is conservative, provided the internal friction is negligible. Assuming friction is negligible, describe changes in the potential energy of a diving board as a swimmer dives from it, starting just before the swimmer steps on the board until just afte

College Physics 1
Problem 10PE (a) How fast must a 3000-kg elephant move to have the same kinetic energy as a 65.0-kg sprinter running at 10.0 m/ s? (b) Discuss how the larger energies needed for the movement of larger animals would relate to metabolic rates.

College Physics 1
Problem 11CQ Define mechanical energy. What is the relationship of mechanical energy to nonconservative forces? What happens to mechanical energy if only conservative forces act?

College Physics 1
Confirm the value given for the kinetic energy of an aircraft carrier in Table \(7.1\). You will need to look up the definition of a nautical mile (\(1\) knot = \(1\) nautical mile/h). Equation Transcription:

College Physics 1
Problem 12CQ What is the relationship of potential energy to conservative force?

College Physics 1
Problem 12PE (a) Calculate the force needed to bring a 950-kg car to rest from a speed of 90.0 km/h in a distance of 120 m (a fairly typical distance for a non-panic stop). (b) Suppose instead the car hits a concrete abutment at full speed and is brought to a stop in 2.00 m. Calculate the force exe

College Physics 1
Consider the following scenario. A car for which friction is not negligible accelerates from rest down a hill, running out of gasoline after a short distance. The driver lets the car coast farther down the hill, then up and over a small crest. He then coasts down that hill into a gas station, where h

College Physics 1
Problem 13PE A cars bumper is designed to withstand a 4.0-km/h (1.1-m/s) collision with an immovable object without damage to the body of the car. The bumper cushions the shock by absorbing the force over a distance. Calculate the magnitude of the average force on a bumper that collapses 0.200 m wh

College Physics 1
Problem 14CQ Describe the energy transfers and transformations for a javelin, starting from the point at which an athlete picks up the javelin and ending when the javelin is stuck into the ground after being thrown.

College Physics 1
Problem 14PE Boxing gloves are padded to lessen the force of a blow. (a) Calculate the force exerted by a boxing glove on an opponents face, if the glove and face compress 7.50 cm during a blow in which the 7.00-kg arm and glove are brought to rest from an initial speed of 10.0 m/s. (b) Calculate t

College Physics 1
Problem 15CQ Do devices with efficiencies of less than one violate the law of conservation of energy? Explain.

College Physics 1
Problem 15PE Using energy considerations, calculate the average force a 60.0-kg sprinter exerts backward on the track to accelerate from 2.00 to 8.00 m/s in a distance of 25.0 m, if he encounters a headwind that exerts an average force of 30.0 N against him.

College Physics 1
Problem 16CQ List four different forms or types of energy. Give one example of a conversion from each of these forms to another form.

College Physics 1
A hydroelectric power facility (see Figure \(7.38\)) converts the gravitational potential energy of water behind a dam to electric energy. (a) What is the gravitational potential energy relative to the generators of a lake of volume \(50.0 \mathrm{~km}^{3}\) ( mass = \(5.00 \times 10^{13} \mathrm{

College Physics 1
Problem 17CQ List the energy conversions that occur when riding a bicycle.

College Physics 1
Problem 17PE (a) How much gravitational potential energy (relative to the ground on which it is built) is stored in the Great Pyramid of Cheops, given that its mass is about 7 109 kg and its center of mass is 36.5 m above the surrounding ground? (b) How does this energy compare with the daily food

College Physics 1
Most electrical appliances are rated in watts. Does this rating depend on how long the appliance is on? (When off, it is a zero-watt device.) Explain in terms of the definition of power.

College Physics 1
Problem 18PE Suppose a 350-g kookaburra (a large kingfisher bird) picks up a 75-g snake and raises it 2.5 m from the ground to a branch. (a) How much work did the bird do on the snake? (b) How much work did it do to raise its own center of mass to the branch?

College Physics 1
Problem 19CQ Explain, 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?

College Physics 1
Problem 19PE In Example 7.7, we found that the speed of a roller coaster that had descended 20.0 m was only slightly greater when it had an initial speed of 5.00 m/s than when it started from rest. This implies that ?PE >> KEi . Confirm this statement by taking the ratio of ?PE to KEi . (Note that

College Physics 1
Problem 20CQ . A spark of static electricity, such as that you might receive from a doorknob on a cold dry day, may carry a few hundred watts of power. Explain why you are not injured by such a spark.

College Physics 1
A \(100-\mathrm{g}\) toy car is propelled by a compressed spring that starts it moving. The car follows the curved track in Figure \(7.39\). Show that the final speed of the toy car is \(0.687 \mathrm{~m} / \mathrm{s}\) if its initial speed is \(2.00 \mathrm{~m} / \mathrm{s}\) and it coasts up the fr

College Physics 1
Explain why it is easier to climb a mountain on a zigzag path rather than one straight up the side. Is your increase in gravitational potential energy the same in both cases? Is your energy consumption the same in both?

College Physics 1
Problem 21PE In a downhill ski race, surprisingly, little advantage is gained by getting a running start. (This is because the initial kinetic energy is small compared with the gain in gravitational potential energy on even small hills.) To demonstrate this, find the final speed and the time taken

College Physics 1
Problem 22CQ Do you do work on the outside world when you rub your hands together to warm them? What is the efficiency of this activity?

College Physics 1
Problem 22PE A 5.00105 -kg subway train is brought to a stop from a speed of 0.500 m/s in 0.400 m by a large spring bumper at the end of its track. What is the force constant k of the spring?

College Physics 1
Problem 23CQ Shivering is an involuntary response to lowered body temperature. What is the efficiency of the body when shivering, and is this a desirable value?

College Physics 1
Problem 23PE A pogo stick has a spring with a force constant of 2.50104 N/m, which can be compressed 12.0 cm. To what maximum height can a child jump on the stick using only the energy in the spring, if the child and stick have a total mass of 40.0 kg? Explicitly show how you follow the steps in th

College Physics 1
Problem 24CQ Discuss the relative effectiveness of dieting and exercise in losing weight, noting that most athletic activities consume food energy at a rate of 400 to 500 W, while a single cup of yogurt can contain 1360 kJ (325 kcal). Specifically, is it likely that exercise alone will be sufficien

College Physics 1
A \(\text { 60.0-kg }\) skier with an initial speed of \(12.0 \mathrm{~m} / \mathrm{s}\) coasts up a \(2.50-\mathrm{m}\) high rise as shown in Figure \(7.40\). Find her final speed at the top, given that the coefficient of friction between her skis and the snow is \(0.0800\). (Hint: Find the distance

College Physics 1
Problem 25CQ What is the difference between energy conservation and the law of conservation of energy? Give some examples of each.

College Physics 1
Problem 25PE (a) How high a hill can a car coast up (engine disengaged) if work done by friction is negligible and its initial speed is 110 km/h? (b) If, in actuality, a 750-kg car with an initial speed of 110 km/h is observed to coast up a hill to a height 22.0 m above its starting point, how much

College Physics 1
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?

College Physics 1
Using values from Table \(7.1\), how many DNA molecules could be broken by the energy carried by a single electron in the beam of an old-fashioned TV tube? (These electrons were not dangerous in themselves, but they did create dangerous x rays. Later model tube TVs had shielding that absorbed x rays

College Physics 1
Problem 27PE Using energy considerations and assuming negligible air resistance, show that a rock thrown from a bridge 20.0 m above water with an initial speed of 15.0 m/s strikes the water with a speed of 24.8 m/s independent of the direction thrown.

College Physics 1
If the energy in fusion bombs were used to supply the energy needs of the world, how many of the \(9\)-megaton variety would be needed for a years supply of energy (using data from Table \(7.1\))? This is not as far-fetched as it may soundthere are thousands of nuclear bombs, and their energy can be

College Physics 1
(a) Use of hydrogen fusion to supply energy is a dream that may be realized in the next century. Fusion would be a relatively clean and almost limitless supply of energy, as can be seen from Table \(7.1\). To illustrate this, calculate how many years the present energy needs of the world could be sup

College Physics 1
The Crab Nebula (see Figure \(7.41\)) pulsar is the remnant of a supernova that occurred in \(\text { A.D. } 1054\). Using data from Table \(7.3\), calculate the approximate factor by which the power output of this astronomical object has declined since its explosion. Figure \(7.41\) Cra

College Physics 1
Suppose a star \(1000\) times brighter than our Sun (that is, emitting \(1000\) times the power) suddenly goes supernova. Using data from Table \(7.3\): (a) By what factor does its power output increase? (b) How many times brighter than our entire Milky Way galaxy is the supernova? (c) Based

College Physics 1
Problem 32PE A person in good physical condition can put out 100 W of useful power for several hours at a stretch, perhaps by pedaling a mechanism that drives an electric generator. Neglecting any problems of generator efficiency and practical considerations such as resting time: (a) How many peopl

College Physics 1
Problem 33PE What is the cost of operating a 3.00-W electric clock for a year if the cost of electricity is $0.0900 per kW?h ?

College Physics 1
Problem 34PE A 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 kW?h ?

College Physics 1
Problem 35PE (a) What is the average power consumption in watts of an appliance that uses 5.00 kW ? h of energy per day? (b) How many joules of energy does this appliance consume in a year?

College Physics 1
Problem 36PE (a) What is the average useful power output of a person who does 6.00106 J of useful work in 8.00 h? (b) Working at this rate, how long will it take this person to lift 2000 kg of bricks 1.50 m to a platform? (Work done to lift his body can be omitted because it is not considered useful

College Physics 1
Problem 37PE A 500-kg dragster accelerates from rest to a final speed of 110 m/s in 400 m (about a quarter of a mile) and encounters an average frictional force of 1200 N. What is its average power output in watts and horsepower if this takes 7.30 s?

College Physics 1
Problem 39PE (a) Find the useful power output of an elevator motor that lifts a 2500-kg load a height of 35.0 m in 12.0 s, if it also increases the speed from rest to 4.00 m/s. Note that the total mass of the counterbalanced system is 10,000 kgso that only 2500 kg is raised in height, but the full

College Physics 1
Problem 40PE (a) What is the available energy content, in joules, of a battery that operates a 2.00-W electric clock for 18 months? (b) How long can a battery that can supply 8.00104 J run a pocket calculator that consumes energy at the rate of 1.0010?3 W ?

College Physics 1
Problem 41PE (a) How long would it take a 1.50105 -kg airplane with engines that produce 100 MW of power to reach a speed of 250 m/s and an altitude of 12.0 km if air resistance were negligible? (b) If it actually takes 900 s, what is the power? (c) Given this power, what is the average force of ai

College Physics 1
Problem 42PE Calculate the power output needed for a 950-kg car to climb a 2.00 slope at a constant 30.0 m/s while encountering wind resistance and friction totaling 600 N. Explicitly show how you follow the steps in the ProblemSolving Strategies for Energy.

College Physics 1
Problem 43PE (a) Calculate the power per square meter reaching Earths upper atmosphere from the Sun. (Take the power output of the Sun to be 4.001026 W.) (b) Part of this is absorbed and reflected by the atmosphere, so that a maximum of 1.30 kW/m2 reaches Earths surface. Calculate the area in km2 o

College Physics 1
(a) How long can you rapidly climb stairs (116/min) on the 93.0 kcal of energy in a 10.0-g pat of butter? (b) How many flights is this if each flight has 16 stairs?

College Physics 1
Problem 45PE (a) What is the power output in watts and horsepower of a 70.0-kg sprinter who accelerates from rest to 10.0 m/s in 3.00 s? (b) Considering the amount of power generated, do you think a well-trained athlete could do this repetitively for long periods of time?

College Physics 1
Calculate the power output in watts and horsepower of a shot-putter who takes \(1.20 \mathrm{~s}\) to accelerate the \(\text { 7.27-kg }\) shot from rest to \(14.0 \mathrm{~m} / \mathrm{s}\), while raising it \(0.800 m\). (Do not include the power produced to accelerate his body.) Figure

College Physics 1
Problem 47PE (a) What is the efficiency of an out-of-condition professor who does 2.10105 J of useful work while metabolizing 500 kcal of food energy? (b) How many food calories would a well-conditioned athlete metabolize in doing the same work with an efficiency of 20%?

College Physics 1
Problem 48PE Energy that is not utilized for work or heat transfer is converted to the chemical energy of body fat containing about 39 kJ/g. How many grams of fat will you gain if you eat 10,000 kJ (about 2500 kcal) one day and do nothing but sit relaxed for 16.0 h and sleep for the other 8.00 h? U

College Physics 1
Problem 49PE Using data from Table 7.5, calculate the daily energy needs of a person who sleeps for 7.00 h, walks for 2.00 h, attends classes for 4.00 h, cycles for 2.00 h, sits relaxed for 3.00 h, and studies for 6.00 h. (Studying consumes energy at the same rate as sitting in class.)

College Physics 1
Problem 50PE What 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.)

College Physics 1
Problem 51PE Shoveling snow can be extremely taxing because the arms have such a low efficiency in this activity. Suppose a person shoveling a footpath metabolizes food at the rate of 800 W. (a) What is her useful power output? (b) How long will it take her to lift 3000 kg of snow 1.20 m? (This cou

College Physics 1
Problem 52PE Very large forces are produced in joints when a person jumps from some height to the ground. (a) Calculate the magnitude of the force produced if an 80.0-kg person jumps from a 0.600m-high ledge and lands stiffly, compressing joint material 1.50 cm as a result. (Be certain to include t

College Physics 1
Problem 53PE Jogging on hard surfaces with insufficiently padded shoes produces large forces in the feet and legs. (a) Calculate the magnitude of the force needed to stop the downward motion of a joggers leg, if his leg has a mass of 13.0 kg, a speed of 6.00 m/s, and stops in a distance of 1.50 cm.

College Physics 1
Problem 54PE (a) Calculate the energy in kJ used by a 55.0-kg woman who does 50 deep knee bends in which her center of mass is lowered and raised 0.400 m. (She does work in both directions.) You may assume her efficiency is 20%. (b) What is the average power consumption rate in watts if she does th

College Physics 1
Kanellos Kanellopoulos flew \(119 \mathrm{~km}\) from Crete to Santorini, Greece, on \(\text { April 23, } 1988\), in the Daedalus \(88\), an aircraft powered by a bicycle-type drive mechanism (see Figure \(7.43\)). His useful power output for the \(\text { 234-min }\) trip was about \(350 W\). Using

College Physics 1
The swimmer shown in Figure \(7.44\) exerts an average horizontal backward force of \(80.0 \mathrm{~N}\) with his arm during each \(1.80 \mathrm{~m}\) long stroke. (a) What is his work output in each stroke? (b) Calculate the power output of his arms if he does \(120\) strokes per minute.

College Physics 1
Problem 57PE Mountain climbers carry bottled oxygen when at very high altitudes. (a) Assuming that a mountain climber uses oxygen at twice the rate for climbing 116 stairs per minute (because of low air temperature and winds), calculate how many liters of oxygen a climber would need for 10.0 h of c

College Physics 1
The awe-inspiring Great Pyramid of Cheops was built more than \(4500\) years ago. Its square base, originally \(230 m\) on a side, covered \(13.1\) acres, and it was \(146 m\) high, with a mass of about \(7 \times 10^{9} \mathrm{~kg}\) . (The pyramids dimensions are slightly different today due to qu

College Physics 1
Problem 59PE (a) How long can you play tennis on the 800 kJ (about 200 kcal) of energy in a candy bar? (b) Does this seem like a long time? Discuss why exercise is necessary but may not be sufficient to cause a person to lose weight.

College Physics 1
Integrated Concepts (a) Calculate the force the woman in Figure \(7.46\) exerts to do a push-up at constant speed, taking all data to be known to three digits. (b) How much work does she do if her center of mass rises \(0.240 m\)? (c) What is her useful power output if she does \(25\) push-up

College Physics 1
(a) A 75.0-kg cross-country skier is climbing a 3.0 slope at a constant speed of 2.00 m/s and encounters air resistance of 25.0 N. Find his power output for work done against the gravitational force and air resistance. (b) What average force does he exert backward on the snow to accomplish this? (c)

College Physics 1
Integrated Concepts The \(\text { 70.0-kg }\) swimmer in Figure \(7.44\) starts a race with an initial velocity of \(1.25 \mathrm{~m} / \mathrm{s}\) and exerts an average force of \(80.0 N\) backward with his arms during each \(1.80 m\) long stroke. (a) What is his initial acceleration if water

College Physics 1
Problem 63PE Integrated Concepts A toy gun uses a spring with a force constant of 300 N/m to propel a 10.0-g steel ball. If the spring is compressed 7.00 cm and friction is negligible: (a) How much force is needed to compress the spring? (b) To what maximum height can the ball be shot? (c) At what an

College Physics 1
Problem 64PE Integrated Concepts (a) What force must be supplied by an elevator cable to produce an acceleration of 0.800 m/s2 against a 200-N frictional force, if the mass of the loaded elevator is 1500 kg? (b) How much work is done by the cable in lifting the elevator 20.0 m? (c) What is the final

College Physics 1
Problem 65PE Unreasonable Results A car advertisement claims that its 900-kg car accelerated from rest to 30.0 m/s and drove 100 km, gaining 3.00 km in altitude, on 1.0 gal of gasoline. The average force of friction including air resistance was 700 N. Assume all values are known to three significan

College Physics 1
Problem 66PE Unreasonable Results Body fat is metabolized, supplying 9.30 kcal/g, when dietary intake is less than needed to fuel metabolism. The manufacturers of an exercise bicycle claim that you can lose 0.500 kg of fat per day by vigorously exercising for 2.00 h per day on their machine. (a) Ho

College Physics 1
Problem 67PE Construct Your Own Problem Consider a person climbing and descending stairs. Construct a problem in which you calculate the long-term rate at which stairs can be climbed considering the mass of the person, his ability to generate power with his legs, and the height of a single stair st

College Physics 1
Problem 68PE Construct Your Own Problem Consider humans generating electricity by pedaling a device similar to a stationary bicycle. Construct a problem in which you determine the number of people it would take to replace a large electrical generation facility. Among the things to consider are the

College Physics 1
Problem 69PE Integrated Concepts A 105-kg basketball player crouches down 0.400 m while waiting to jump. After exerting a force on the floor through this 0.400 m, his feet leave the floor and his center of gravity rises 0.950 m above its normal standing erect position. (a) Using energy consideratio