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Conceptual Physics 12th edition Paul G. Hewitt - Solutions

Discuss how the conservation of momentum is a consequence of Newton's third law?
Most often we say that force causes acceleration. But when Evan took a ride in a rocket sled at Bonneville Salt Flats, blood was forced to the back of his brain, nearly blacking him out. Discuss and identify the cause of this force.
To tighten a bolt, you push with a force of 80 N at the end of a wrench handle that is 0.25 m from the axis of the bolt.a. What torque are you exerting?b. You move your hand inward to be only 0.10 m from the bolt. To achieve the same torque, show that you should exert 200 N of force.c. Do your
In one of the photos at the beginning of this chapter, Mary Beth uses a torque feeler that consists of a meter stick held at the 0-cm end with a weight dangling from various positions along the stick. When the stick is held horizontally, torque is produced when a 1-kg object hangs from the 50-cm
Stand on a bathroom scale on a level floor, and the reading on the scale shows the gravitational force on you, mg. If the floor is slanted at an angle, the scale reading will be less than mg. Discuss why this is so, and why it is a good idea to measure your weight when the scale is on a horizontal
Suppose you jounce up and down while weighing yourself on your bathroom scale. The weight reading likewise "jounces up and down." Does this mean that the force of gravity, mg, varies when you jounce?
Is there a torque about the Moon's center of mass when the Moon's long axis is aligned with Earth's gravitational field? Explain how this compares with a magnetic compass.
Would ocean tides exist if the gravitational pull of the Moon (and the Sun) were somehow equal on all parts of the world? Explain.
With respect to spring and neap ocean tides, when are the tides lowest? That is, which tide is best for digging clams?
With a stick and strings, make a "trajectory stick" as shown on page 187.
With your friends, whirl a bucket of water in a vertical circle fast enough so that the water doesn't spill out. As it happens, the water in the bucket is falling, but with less speed than you give to the bucket. Tell how your bucket swing relates to satellite motion-that satellites in orbit
Bull's-eye Bob at a hunting range fires his rifle at a target 200 meters downrange. The bullet moves horizontally from the rifle barrel with a speed of 400 m/s. (a) How far does the bullet drop from a straight-line horizontal path by the time it reaches the target? (b) To hit a bull's-eye why does
Two golfers each hit a ball at the same speed, but one at 60° with the horizontal and the other at 30°. Which ball goes farther?
Which planets have a more-than-one-Earth-year period: planets nearer than Earth to the Sun, or planets farther from the Sun than Earth?
In the sketch on the left, a ball gains KE when rolling down a hill because work is done by the component of weight (F) that acts in the direction of motion. Sketch in the similar component of gravitational force that does work to change the KE of the satellite on the right.
What is the shape of the orbit when the velocity of the satellite is everywhere perpendicular to the force of gravity?
What is the maximum possible speed of impact on the surface of Earth for a faraway body initially at rest that falls to Earth by virtue of Earth's gravity only?
At what point in its elliptical orbit about the Sun is the acceleration of Earth toward the Sun a maximum? At what point is it a minimum? Defend your answers.
Mars has about 19 the mass of Earth. If Mars were somehow positioned into the same orbit as Earth's, discuss how its time to circle the Sun would compare with Earth's. (Longer, shorter, or the same?)
A communications satellite with a 24-hour period hovers over a fixed point on Earth and, to Earth observers, seems motionless. Why is it placed only in an orbit in the plane of Earth's equator? In your discussion, think of the satellite's orbit as a ring around Earth.
Which two planets are never seen at midnight, and why?
Why does a satellite burn up when it descends into the atmosphere? And why doesn't it burn up when it ascends through the atmosphere?
Discuss the requirement that a GPS device needs information from at least three GPS satellites and why one "very good" satellite cannot do the task?
A giant rotating wheel in space provides artificial gravity for its occupants, as discussed in Chapter 8. Instead of a full wheel, discuss the idea of a pair of capsules joined by a tether line and rotating about each other. Can such an arrangement provide artificial gravity for the occupants?
The average speed of a perfume-vapor molecule at room temperature may be about 300 m/s, but you'll find the speed at which the scent travels across the room is much less. Why?
What evidence can you cite for the microscopic crystal nature of certain solids? For the macroscopic crystal nature?
Greta Novak is treated to remarkable flotation in the very-salty Dead Sea. How does the buoyant force on her compare when she is floating in fresh water? In answering this question, discuss differences in the volume of water displaced in the two cases.
Would buoyancy occur in the absence of weight? Discuss the buoyancy that would or wouldn't occur in the International Space Station.
Why do the gondolas of the Falkirk Wheel (see Figure 13.19) have the same weight whether or not they carry boats?
Float a water-soaked Ping-Pong ball in a can of water held more than a meter above a rigid floor. Then drop the can. Careful inspection will show that the ball was pulled beneath the surface as both the ball and the can drop. (What does this say about surface tension?) More dramatically, when the
A 12-kg piece of metal displaces 2 L of water when submerged. Show that its density is 6000 kg/m3. How does this compare with the density of water?
A 1-m-tall barrel is closed on top except for a thin pipe extending 5 m up from the top. When the barrel is filled with water up to the base of the pipe (1 meter deep), the water pressure on the bottom of the barrel is 10 kPa. What is the pressure on the bottom when water is added to fill the pipe
In the hydraulic pistons shown in the sketch, the small piston has a diameter of 2 cm. The large piston has a diameter of 6 cm. How much more force can the larger piston exert compared with the force applied to the smaller piston?
Why is it easier to float in salt water than in fresh water?
Discuss whether or not lower pressure is the result of fast-moving air, or fast-moving air is the result of lower pressure. Give one example supporting each point of view. (In physics, when two things are related-such as force and acceleration or speed and pressure-it is usually arbitrary which one
Will Maynez burns a 0.6-g peanut beneath 50 g of water, which increases in temperature from 22°C to 50°C. (The specific heat capacity of water is 1.0 cal/g · °C.)a. Assuming that 40% of the heat released by the burning peanut makes its way to the water (40% efficiency), show that the peanut's
If you wish to warm 50 kg of water by 20°C for your bath, show that the amount of heat needed is 1000 kcal (1000 Cal). Then show that this is equivalent to about 4200 kJ.
The specific heat capacity of steel is 450 J/kg · °C. Show that the amount of heat needed to raise the temperature of a 10-kg piece of steel from 0°C to 100°C is 450,000 J. How does this compare with the heat needed to raise the temperature of the same mass of water through the same temperature
Consider a bar 1 m long that expands 0.6 cm when heated. Show that when similarly heated, a 100-m bar of the same material becomes 100.6 m long.
Rank the magnitudes of these units of thermal energy from greatest to least: a. 1 calorie b. 1 Calorie c. 1 joule
Wrap a piece of paper around a thick metal bar and place it in a flame.Notice that the paper will not catch fire. Can you explain this in terms of the conductivity of the metal bar? (Paper generally will not ignite until its temperature reaches about 230°C.)
Why is it incorrect to say that, when a hot object warms a cold one, the increase in temperature of the cold one is equal to the decrease in temperature of the hot one? When is this statement correct?
Discuss why a 1-ft2 hole in a ceiling that admits sunlight when the Sun is overhead is like having a 100-W bulb in the room. Assume the atmosphere reduces solar energy at Earth's surface as 1.0 kW/m2.
Discuss what is meant by the saying "You can never change only one thing." Use a mathematical equation to make your point?
In what way did the Industrial Era contribute to climate change? Discuss better uses of fossil fuels than creating heat and smoke.
Why does water vapor in the air condense when the air is chilled?
Air-conditioning units contain no water whatever, yet it is common to see water dripping from them when they're operating on a hot day? Discuss.
Watch the spout of a teakettle of boiling water. Notice that you cannot see the steam that issues from the spout. The cloud that you see farther away from the spout is not steam but condensed water droplets. Now hold the flame of a candle in the cloud of condensed steam. Can you explain your
You can make rain in your kitchen. Put a cup of water in a Pyrex saucepan or a glass coffeemaker and heat it slowly over a low flame. When the water is warm, place a saucer filled with ice cubes on top of the container. As the water below is heated, droplets form at the bottom of the cold saucer
When you step inside a warm ski lodge on a cold day, your eyeglasses fog up. Why does this occur?
Show that the ideal efficiency is 90% for an engine in which fuel is heated to 3000 K and the surrounding air is 300 K?Ideal efficiency = Tbot - Tcold / Thot
Calculate the ideal efficiency of an engine in which fuel is heated to 2700 K and the surrounding air is 200 K?
What is the ideal efficiency of an automobile engine that operates between the temperatures 600°C and 320°C? (Why is your answer not 47%?)
Consider a 6.0-g steel nail 8.0 cm long and a hammer that exerts an average force of 600 N on the nail when it is being driven into a piece of wood. The nail becomes warmer. Show that the increase in the nail's temperature is 17.8°C. (Assume that the specific heat capacity of steel is 450 J/kg (
How does the ideal efficiency of an automobile relate to the temperature of the engine and the temperature of the environment in which it operates? Be specific.
Strictly speaking, why will a refrigerator that contains a fixed amount of food consume more energy in a warm room than in a cold room?
Hovering over the surface of our skin is a layer of air some 3 millimeters in thickness that acts as a thermal blanket. On a hot day, what effect does a breeze on bare skin have on your skin? What effect does it have on a cold day?
The temperature in Boston was 40°F when it was 80°F in St. Petersburg, FL. What is your response to a friend who suggests that it was twice as hot in St. Petersburg on that day?
A banjo player plucks the middle of a string pinned down at both ends. Where are the nodes of the standing wave in the string? What is the wavelength of the vibrating string?
If the speed of sound were dependent on its frequency, would you enjoy a concert sitting in the second balcony? Explain. Discuss.
Discuss why sound travels faster in moist air. (Note that at the same temperature, water vapor molecules have the same average kinetic energy as the heavier nitrogen and oxygen molecules in the air.) How, then, do the average speeds of H2O molecules compare with the speeds of N2 and O2 molecules?
After inhaling helium gas, a person talks with a high pitched voice. One of the reasons for this is the higher speed of sound in helium than in air. Why does sound travel faster in helium?
Strictly speaking, when an object acquires a positive charge by the transfer of electrons, what happens to its mass? Discuss what happens to its mass when it acquires a negative charge.
A balloon may easily be charged to several thousand volts. Does that mean it has several thousand joules of energy? Explain.
Two point charges, each with 0.1 C of charge, are 0.1 m apart. Given that k = 9.0 × 109 N·m2/C2 (the proportionality constant for Coulomb's law), show that the force between the charges is 9.0 × 109 N.
Why aren't objects with vast numbers of electrons normally electrically charged?
A crystal of salt consists of negative and positive ions. How does the net charge of the negative ions compare with that of the positive ions? Explain.
The proportionality constant k in Coulomb's law is huge in ordinary units, whereas the proportionality constant G in Newton's law of gravitation is tiny. What does this indicate about the relative strengths of these two forces? Discuss.
If you rub an inflated balloon against your hair and place the balloon against a door, what mechanism causes it to stick? Explain.
To connect a pair of resistors so that their combined (equivalent) resistance will be less than the resistance of either one, should you connect them in series or in parallel?
(a) What single resistor would be equivalent to the resistors in this arrangement?(b) If 24 volts were applied across points A and B, how much current would there be in the circuit?(c) How much current in the 12-ohm resistor?
Three 6-ohm resistors are arranged in a triangle as shown. A voltage source of 12 V is impressed across one of the resistors.(a) How much current is in that resistor?(b) How much current is in each of the other two resistors?(c) How much current is in the voltage source?(d) What is the equivalent
A tipped domino sends a pulse along a row of standing dominoes. Is this a good analogy for the way electric current, sound, or both travel?
The damaging effects of electric shock result from the amount of current that flows in the body. Why, then, do we see signs that read "Danger-High Voltage" rather than "Danger-High Current"
In what sense are all magnets electromagnets? Discuss.
By what mechanism do the iron filings shown about the magnet in Figure 24.2 align with the magnetic field?Figure 24.2
Earth's magnetic field induces some degree of magnetism in most of the iron objects around you. With a compass you can see that cans of food on your pantry shelf have north and south poles. When you pass the compass from their bottoms to their tops, you can easily identify their poles. Mark the
Drop a small bar magnet through a vertical plastic pipe, noting its speed of fall. Then do the same with a copper pipe. Whoa! Why the difference?
A transformer for a laptop computer converts a 120-V input to a 24-V output. Show that the primary coil has five times as many turns as the secondary coil.
If the output current for the transformer in the preceding problem is 1.8 A, show that the input current is 0.36 A.
An ideal transformer has 50 turns in its primary and 250 turns in its secondary. 12-V ac is connected to the primary. Show that (a) 60 V ac is available at the secondary; (b) 6 A of current is in a 10-Ω device connected to the secondary; (c) The power supplied to the primary is 360
A power of 100 kW (105 W) is delivered to the other side of a city by a pair of power lines, between which the voltage is 12,000 V.(a) Use the formula P = IV to show that the current in the lines is 8.3 A.(b) If each of the two lines has a resistance of 10 Ω, show that there is a 83-V change of
Why will more voltage be induced with the apparatus shown above if an iron core is inserted in the coils? Discuss.
What is the principal difference between a step-up transformer and a step-down transformer?
A 120-volt ac source powers the circuit shown. How many volts are impressed across the lightbulb, and how many amps flow through it?
Your physics instructor drops a magnet through a long vertical copper pipe and it moves slowly compared with the drop of a nonmagnetized object. Provide an explanation.
This exercise is similar to the preceding one. Why will a bar magnet fall slower and reach terminal velocity in a vertical copper or aluminum tube but not in a cardboard tube?
In 1676, the Danish astronomer Ole Roemer had one of those "aha" moments in science. He concluded from accumulated observations of eclipses of Jupiter's moon at different times of the year that light must travel at finite speed and needed 1300 s to cross the diameter of Earth's orbit around the
The diameters of the circles that make up the solar images in Dean's photo are about 1/100 the distance to the openings in the leaves that cast the spots. That means 100 circles placed end to end would extend from each spot to the opening that casts the spot. How does this tell you how many Suns
Paul Doherty, also in the chapter-opening photos, displays images of an annular eclipse. Note that the images are full circular outlines. At this special time, is the average distance of the Moon from Earth closer, farther, or its usual distance?
Why does the Sun look reddish at sunrise and sunset but not at noon?
Very big particles, like droplets of water, absorb more radiation than they scatter. How does this relate to the darkness of rain clouds? Discuss.
Why can't we see stars in the daytime?
Poke a hole in a piece of paper, hold it in sunlight so that the solar image is the same size as a coin on the ground, and then determine how many coins would fit between the ground and the pinhole. That's the same number of solar diameters that would fit in the distance from Earth to the Sun.
Why do older people who do not wear glasses read books farther away from their eyes than younger people do?
When Stephanie Hewitt dips a glass rod into vegetable oil, the submerged part of the rod is invisible. What does this say about the relative speeds of light in the glass and in the oil? Or asked another way, how do the indices of refraction, n, compare for the glass and oil?
To reduce glare from the surroundings, the windows of some department stores, rather than being vertical, slant inward at the bottom. Discuss why this reduces glare.
What role do polarization filters play in 3-D projection?
Light will not pass through a pair of Polaroid sheets when they are aligned perpendicularly. However, if a third Polaroid is sandwiched between the two with its alignment halfway between the alignments of the other two (that is, with its axis making a 45° angle with each of the other two alignment
When only a few photons are observed, classical physics fails. When many are observed, classical physics is valid. Which of these two facts is consistent with the correspondence principle?

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