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College Physics

Hugh D. Young

Chapter 1

Models, Measurements, and Vectors

Educators


Problem 1

(a) The maximum sodium intake for a person on a 2000 calorie diet should be 2400 mg/day. How many grams of sodium is this per day? (b) The recommended daily allowance (RDA) of the trace element chromium is 120$\mu g /$ day. Express this dose in
considered safe (although the safety of higher doses has not yet been established. Express this intake in grams per day. (d) The electrical resistance of the human body is approximately 1500 ohms when it is dry. Express this resistance in kilohms.
(e) An electrical current of about 0.020 amp can cause muscular spasms so that a person cannot, for example, let go of a wire with that amount of current. Express this current in milliamps.

Bruce E.
Numerade Educator

Problem 2

(a) How many ohms are there in a 7.85 -megohm resistor?
(b) Typical laboratory capacitors are around 5 picofarads. How many farads are they? (c) The speed of light in vacuum is $3.00 \times 10^{8} \mathrm{m} / \mathrm{s} .$ Express this speed in gigameters per second. (d) The wavelength of visible light is between 400 $\mathrm{nm}$ and 700 $\mathrm{nm} .$ Express this wavelength in meters. (e) The diameter of a typical atomic nucleus is about 2 femtometers. Express this diameter in meters.

Veronica P.
Numerade Educator

Problem 3

(a) The recommended daily allowance (RDA) of the trace metal magnesium is 410 $\mathrm{mg} / \mathrm{day}$ for males. Express this quantity in $\mu \mathrm{g} / \mathrm{day} .$ (b) For adults, the RDA of the amino acid lysine is 12 $\mathrm{mg}$ per kg of body weight. How many grams per day should a 75 $\mathrm{kg}$ adult receive? (c) A typical multivitamin tablet can contain 2.0 $\mathrm{mg}$ of vitamin $\mathrm{B}_{2}$ (riboflavin), and the RDA is 0.0030 $\mathrm{g} / \mathrm{day} .$ How many such tablets should a person take each day to get the proper amount of this vitamin, assuming that he gets none from any other sources? (d) The RDA for the trace element selenium is 0.000070 $\mathrm{g} /$ day. Express this dose in mg/day.

Bruce E.
Numerade Educator

Problem 4

$\bullet$ (a) Starting with the definition 1.00 in. $=2.54 \mathrm{cm},$ find the number of kilometers in 1.00 mile. (b) In medicine, volumes are often expressed in milliliters (ml or mL). Show that a milliliter is the same as a cubic centimeter. (c) How many cubic centimeters of water are there in a 1.00 L bottle of drinking water?

Veronica P.
Numerade Educator

Problem 5

$\bullet($ a) The density (mass divided by volume) of water is 1.00 $\mathrm{g} / \mathrm{cm}^{3} .$ What is this value in kilograms per cubic meter? (b) The density of blood is 1050 $\mathrm{kg} / \mathrm{m}^{3} .$ What is this density in $\mathrm{g} / \mathrm{cm}^{3} ?(\mathrm{c})$ How many kilograms are there in a 1.00 $\mathrm{L}$ bottle of drinking water? How many pounds?

Bruce E.
Numerade Educator

Problem 6

$\bullet$ Calculate the earth's speed in its orbit around the sun, in $\mathrm{m} / \mathrm{s}, \mathrm{km} / \mathrm{h}$ and $\mathrm{mi} / \mathrm{h},$ using information from Appendices $\mathrm{D}$ and $\mathrm{E} .$

Veronica P.
Numerade Educator

Problem 7

$\bullet$ How many nanoseconds does it take light to travel 1.00 $\mathrm{ft}$ in vacuum? (This result is a useful quantity to remember.)

Bruce E.
Numerade Educator

Problem 8

Metric wrenches. (a) You have a new set of metric wrenches, but need to loosen a $\frac{3}{8}$ inch bolt. To find out which size metric wrench to use, convert the $\frac{3}{8}$ in. to millimeters, accurate to the
nearest tenth of a millimeter. (b) If you want to tighten a 12 $\mathrm{mm}$ bolt, what size wrench should you use in inches, accurate to the nearest hundredth of an inch? (c) English-unit wrenches often
come in $\frac{1}{8}$ inch intervals, not in decimal units. What size wrench should you use in part (b)?

Veronica P.
Numerade Educator

Problem 9

$\bullet$ Gasoline mileage. You are considering buying a European car and want to see if its advertised fuel efficiency (expressed in $\mathrm{km} / \mathrm{L} )$ is better than that of your present car. If your car gets 37.5 miles per gallon, how many $\mathrm{km} / \mathrm{L}$ is this? Consult Appendix D.

Bruce E.
Numerade Educator

Problem 10

$\bullet$ While driving in an exotic foreign land, you see a speed-limit sign on a highway that reads $180,000$ furlongs per fort-night. How many miles per hour is this? (One furlong is $\frac{1}{8}$ mile,
and a fortnight is 14 days. A furlong originally referred to the length of a plowed furrow.)

Veronica P.
Numerade Educator

Problem 11

$\bullet$ Fill 'er up! You fill up your gas tank in Europe when the euro is worth $\$ 1.25$ and gasoline costs 1.35 euros per liter. What is the cost of gasoline in dollars per gallon? How does your answer compare with the cost of gasoline in the United States? (Use conversion factors in Appendix D.)

Bruce E.
Numerade Educator

Problem 12

$\bullet$ Bacteria. Bacteria vary somewhat in size, but a diameter of 2.0$\mu \mathrm{m}$ is not unusual. What would be the volume (in cubic centimeters) and surface area (in square millimeters) of such a bacterium, assuming that it is spherical? (Consult Chapter 0 for relevant formulas.)

Veronica P.
Numerade Educator

Problem 13

$\cdot$ Compute the number of seconds in (a) an hour, (b) a 24 hour day, and (c) a 365 day year.

Bruce E.
Numerade Educator

Problem 14

$\bullet$ Some commonly occurring quantities. All of the quantities that follow will occur frequently in your study of physics. (a) Express the speed of light $\left(3.00 \times 10^{8} \mathrm{m} / \mathrm{s}\right)$ in $\mathrm{mi} / \mathrm{s}$ and mph. (b) Find the speed of sound in air at $0^{\circ} \mathrm{C}(1100 \mathrm{ft} / \mathrm{s})$ in $\mathrm{m} / \mathrm{s}$ and mph. (c) Show that 60 $\mathrm{mph}$ is the same as 88 $\mathrm{ft} / \mathrm{s}$ . (d) Convert the acceleration of a freely falling body $\left(9.8 \mathrm{m} / \mathrm{s}^{2}\right)$ to $\mathrm{ft} / \mathrm{s}^{2}$

Veronica P.
Numerade Educator

Problem 15

$\cdot$ Express each of the following numbers to three, five, and eight significant figures: (a) $\pi=3.141592654 \ldots,$ (b) $e=$ $2.718281828 \ldots,(\mathrm{c}) \sqrt{13}=3.605551275 \ldots$

Bruce E.
Numerade Educator

Problem 16

$\cdot$ Express each of the following approximations of $\pi$ to six significant figures: (a) $22 / 7,($ b) 35$/ 113 .$ (c) Are these approximations accurate to that precision?

Veronica P.
Numerade Educator

Problem 17

$\cdot$ An angle is given, to one significant figure, as $4^{\circ},$ meaning that its value is between $3.5^{\circ}$ and $4.5^{\circ} .$ Find the corresponding range of possible values of $(a)$ the cosine of the angle, (b) the sine of the angle, and (c) the tangent of the angle.

Bruce E.
Numerade Educator

Problem 18

$\cdot$ Blood is thicker than water. The density (mass divided by volume) of pure water is $1.00 \mathrm{g} / \mathrm{cm}^{3},$ that of whole blood is $1.05 \mathrm{g} / \mathrm{cm}^{3},$ and the density of seawater is 1.03 $\mathrm{g} / \mathrm{cm}^{3} .$ What is the mass (in grams) of 1.00 $\mathrm{L}$ of each of these substances?

Veronica P.
Numerade Educator

Problem 19

$\bullet$ White dwarfs and neutron stars. Recall that density is mass divided by volume, and consult Chapter 0 and Appendix $E$ as needed. (a) Calculate the average density of the earth in $g / c m^{3},$ assuming our planet to be a perfect sphere. (b) In about 5 billion years, at the end of its lifetime, our sun will end up as a white dwarf, having about the same mass as it does now, but reduced to about $15,000 \mathrm{km}$ in diameter. What will be its density at that stage? (c) A neutron star is the remnant left after certain supernovae (explosions of giant stars). Typically, neutron stars are about 20 $\mathrm{km}$ in diameter and have around the same mass as our sun. What is a typical neutron star density in $\mathrm{g} / \mathrm{cm}^{3} ?$

Bruce E.
Numerade Educator

Problem 20

Atoms and nuclei. The atom helium (He) consists of two protons, two neutrons, and two electrons. (Recall that density is mass divided by volume, and consult Appendices $A$ and $E$ and Table 1.1 as needed.) (a) The diameter of the He atom is approximately 0.10 nm. Calculate the density of the He atom in $\mathrm{g} / \mathrm{cm}^{3}$ (assuming that it is a sphere), and compare it with that of pure water, which is 1.0 $\mathrm{g} / \mathrm{cm}^{3}$ . (b) The diameter of the He nucleus is about 2.0 fm. Assuming the nucleus to be a sphere, calculate its density in $\mathrm{g} / \mathrm{cm}^{3}$ and compare it with that of a neutron star in the previous exercise.

Veronica P.
Numerade Educator

Problem 21

Critical mass of neptunium. In the fall of $2002,$ a group of scientists at Los Alamos National Laboratory determined that the critical mass of neptunium-237 is about 60.0 $\mathrm{kg}$ . (The critical mass of a fissionable material is the minimum amount that must be brought together to start a nuclear chain reaction.) Neptunium has a density of 19.5 $\mathrm{g} / \mathrm{cm}^{3} .$ What would be the radius of a sphere made of this material that has a critical mass? (Recall that density is mass divided by volume.)

Bruce E.
Numerade Educator

Problem 22

\bullet Cell walls. Although these quantities vary from one type of cell to another, a cell can be 2.0$\mu \mathrm{m}$ in diameter with a cell wall 50.0 $\mathrm{nm}$ thick. If the density (mass divided by volume) of the wall material is the same as that of pure water, what is the mass (in mg) of the cell
wall, assuming the cell to be spherical and the wall to be a very thin spherical shell?

Veronica P.
Numerade Educator

Problem 23

\bullet A brass washer has an outside diameter of 4.50 $\mathrm{cm}$ with a hole of
diameter 1.25 $\mathrm{cm}$ and is 1.50 $\mathrm{mm}$ thick. (See Figure $1.21 . )$ The density
of brass is 8600 $\mathrm{kg} / \mathrm{m}^{3} .$ If you put this washer on a laboratory balance, what will it "weigh" in grams? (Recall that density is mass divided by volume and consult Chapter 0 as needed. $)$

Bruce E.
Numerade Educator

Problem 24

$\cdot$ Estimate the total mass of all the humans presently living on earth.

Veronica P.
Numerade Educator

Problem 25

$\bullet$ How many words are there in this book?

Bruce E.
Numerade Educator

Problem 26

$\bullet$ How many cells in the body? Although their sizes vary, cells can be modeled as spheres 2.0$\mu \mathrm{m}$ in diameter, on the average. About how many cells does a typical human contain,
and approximately what is the mass of an average cell?

Veronica P.
Numerade Educator

Problem 27

$\cdot$ How many times does a typical person blink her eyes in a lifetime?

Bruce E.
Numerade Educator

Problem 28

You are using water to dilute small amounts of chemicals in the laboratory, drop by drop. How many drops of water are in a 1.0 bottle? (Hint: Start by estimating the diameter of a drop of water.)

Veronica P.
Numerade Educator

Problem 29

How many dollar bills would you have to stack to reach the moon? Would that be a cheaper way to get there than building and launching a spacecraft (which costs a few billion dollars)?

Bruce E.
Numerade Educator

Problem 30

Space station. You are designing a space station and want to get some idea how large it should be to provide adequate air for the astronauts. Normally, the air is replenished, but for security, you decide that there should be enough to last for two weeks in case of a malfunction. (a) Estimate how many cubic
meters of air an average person breathes in two weeks. A typical human breathes about 1$/ 2 \mathrm{L}$ per breath. (b) If the space station is to be spherical, what should be its diameter to contain
all the air you calculated in part (a)?

Veronica P.
Numerade Educator

Problem 31

A beating heart. How many times does a human heart beat during a lifetime? How many gallons of blood does it pump in that time if, on the average, it pumps 50 $\mathrm{cm}^{3}$ of blood with each beat?

Bruce E.
Numerade Educator

Problem 32

$\bullet$ How long would it take you to walk to the moon, and how many steps would you have to take, assuming that you could somehow walk normally in space?

Veronica P.
Numerade Educator

Problem 33

.. How much would it cost to paper the entire United States (including Alaska and Hawaii) with dollar bills? What would be the cost to each person in the nation?

Bruce E.
Numerade Educator

Problem 34

$\cdot$ On a single diagram, carefully sketch each force vector to scale and identify its magnitude and direction on your drawing: (a) 60 lb at $25^{\circ}$ east of north. (b) 40 lb at $\pi / 3$ south of west.
(c) 100 lb at $40^{\circ}$ north of west. (d) 50 lb at $\pi / 6$ east of south.

Veronica P.
Numerade Educator

Problem 35

$\bullet$ Hearing rattles from a snake, you make two rapid displacements of magnitude 1.8 $\mathrm{m}$ and 2.4 $\mathrm{m} .$ In sketches (roughly to scale), show how your two displacements might add up to give a resultant of magnitude (a) $4.2 \mathrm{m} ;$ (b) $0.6 \mathrm{m} ;$ (c) 3.0 $\mathrm{m} .$

Bruce E.
Numerade Educator

Problem 36

A ladybug starts at the center of a 12 -in.-diameter turntable and crawls in a straight radial line to the edge. While this is happening, the turntable turns through a $45^{\circ}$ angle. (a) Draw a sketch showing the bug's path and the displacement vector for the bug's progress. (b) Find the magnitude and direction of the ladybug's displacement vector.

Veronica P.
Numerade Educator

Problem 37

$\bullet$ For the vectors $\vec{A}$ and $\vec{B}$ shown in Figure $1.22,$ carefully sketch (a) the vector sum $\vec{A}+\vec{B} ;$ (b) the vector difference $\vec{A}-\vec{B} ;$ (c) the vector $-\vec{A}-\vec{B} ;(\mathrm{d})$ the vector difference $\vec{\boldsymbol{B}}-\vec{\boldsymbol{A}}$

Bruce E.
Numerade Educator

Problem 38

$\bullet$ Chin brace. A person with an injured jaw has a brace below his chin. The brace is held in place by two cables directed at $65^{\circ}$ above the horizontal. (See Figure $1.23 . )$ The cables produce forces of equal magnitude having a vertical resultant of 2.25 $\mathrm{N}$ upward. (a) Make a scale drawing showing both the forces produced by the cables and the resultant force. Estimate the angle carefully or measure it with a protractor. (b) Use your scale drawing to estimate the magnitude of the
force due to each cable.

Veronica P.
Numerade Educator

Problem 39

A rocket fires two engines simultaneously. One produces a thrust of 725 $\mathrm{N}$ directly forward, while the other gives a $513-\mathrm{N}$ thrust at $32.4^{\circ}$ above the forward, while the other gives a $513-\mathrm{N}$ and direction (relative to the forward direction) of the resultant force that these engines exert on the rocket.

Bruce E.
Numerade Educator

Problem 40

$\cdot$ In each of the cases that follow, the magnitude of a vector is given along with the counterclockwise angle it makes with the $+x$ axis. Use trigonometry to find the $x$ and $y$ components of the vector. Also, sketch each vector approximately to scale to see if your calculated answers seem reasonable. (a) 50.0 $\mathrm{N}$ at $60.0^{\circ},(\mathrm{b}) 75 \mathrm{m} / \mathrm{s}$ at $5 \pi / 6 \mathrm{rad},(\mathrm{c}) 254 \mathrm{lb}$ at $325^{\circ},$ (d) 69 $\mathrm{km}$ at 1.1$\pi \mathrm{rad} .$

Veronica P.
Numerade Educator

Problem 41

$\cdot$ In each of the cases that follow, the components of a vector $\vec{A}$ are given. Use trigonometry to find the magnitude of that vector and the counterclockwise angle it makes with the $+x$ axis. Also, sketch each vector approximately to scale to see if your calculated answers seem reasonable. (a) $A_{x}=4.0 \mathrm{m}, A_{y}=5.0 \mathrm{m},$ (b) $A_{x}=-3.0 \mathrm{km}, A_{y}=-6.0 \mathrm{km},(\mathrm{c}) A_{x}=9.0 \mathrm{m} / \mathrm{s}, A_{y}=$ $-17 \mathrm{m} / \mathrm{s},(\mathrm{d}) A_{x}=-8.0 \mathrm{N}, A_{\mathrm{y}}=12 \mathrm{N}$

Bruce E.
Numerade Educator

Problem 42

$\bullet$ A woman takes her dog Rover for a walk on a leash. To get the little pooch moving forward, she pulls on the leash with a force of 20.0 $\mathrm{N}$ at an angle of $37^{\circ}$ above the horizontal. (a) How much force is tending to pull Rover forward? (b) How much force is tending to lift Rover off the ground?

Veronica P.
Numerade Educator

Problem 43

If a vector $\vec{A}$ has the following components, use trigonometry to find its magnitude and the counterclockwise angle it makes with the $+x$ axis: (a) $A_{x}=8.0$ lb, $A_{y}=6.0$ lb (b) $A_{x}=-24 \frac{m}{s}, A_{y}=-31 \frac{m}{s}$ (c) $A_{x}=-1500$ km, $A_{y}=2000$ km (d) $A_{x}=71.3$ N, $A_{y}=-54.7$ N

Bruce E.
Numerade Educator

Problem 44

Compute the $x$ and $y$ components of the vectors $\vec{A}, \vec{B}$ and $\vec{C}$ shown in Figure 1.24

Veronica P.
Numerade Educator

Problem 45

Vector $A$ has components $A_{x}=1.30 \mathrm{cm}, \quad A_{y}=$ $2.25 \mathrm{cm} ; \quad$ vector $\vec{B}$ has components $B_{x}=4.10 \mathrm{cm}$ $B_{y}=-3.75 \mathrm{cm} .$ Find $(\mathrm{a})$ the components of the vector sum $A+B ;$ (b) the magnitude and direction of $\vec{A}+\vec{B}$ (c) the components of the vector difference $\vec{B}-\vec{A}$ (d) the magnitude and direction of $\vec{\boldsymbol{B}}-\vec{\boldsymbol{A}}$

Bruce E.
Numerade Educator

Problem 46

. A plane leaves Seattle, flies 85 mi at $22^{\circ}$ north of east, and then changes direction to $48^{\circ}$ south of east. After flying at 115 mi in this new direction, the pilot must make an emergency
landing on a field. The Seattle airport facility dispatches a rescue crew. (a) In what direction and how far should the crew fly to go directly to the field? Use components to solve this problem. (b) Check the reasonableness of your answer with a careful graphical sum.

Veronica P.
Numerade Educator

Problem 47

$\bullet$ You're hanging from a chinning bar, with your arms at right angles to each other. The magnitudes of the forces exerted by both your arms are the same, and together they exert just enough upward force to support your weight, 620 $\mathrm{N}$ . (a) Sketch the two force vectors for your arms, along with their resultant, and (b) use components to find the magnitude of each of the two "arm" force vectors.

Bruce E.
Numerade Educator

Problem 48

$\bullet$ Three horizontal ropes are attached to a boulder and produce the pulls shown in Figure $1.25 .$ (a) Find the $x$ and $y$ components of each pull. (b) Find the components of the resultant of the three pulls. (c) Find the magnitude and direction (the counterclockwise angle with the $+x$ axis ) of the resultant pull. (d) Sketch a clear graphical sum to check your answer in part (c).

Veronica P.
Numerade Educator

Problem 49

A disoriented physics professor drives 3.25 $\mathrm{km}$ north, then 4.75 $\mathrm{km}$ west, and then 1.50 $\mathrm{km}$ south. (a) Use components to find the magnitude and direction of the resultant displacement of this professor. (b) Check the reasonableness of your answer with a graphical sum.

Bruce E.
Numerade Educator

Problem 50

$\cdot$ A postal employee drives a delivery truck along the route shown in Figure $1.26 .$ Use components to determine the magnitude and direction of the truck's resultant displacement. Then check the reasonableness of your answer by sketching a graphical sum.

Veronica P.
Numerade Educator

Problem 51

Baseball mass. Baseball rules specify that a regulation ball shall weigh no less than 5.00 ounces nor more than 5$\frac{1}{4}$ ounces. What are the acceptable limits, in grams, for a regulation ball? (See Appendix D and use the fact that 16 oz $=1$ lb.)

Bruce E.
Numerade Educator

Problem 52

As you eat your way through a bag of chocolate chip cookies, you observe that each cookie is a circular disk with a diameter of 8.50 $\mathrm{cm}$ and a thickness of 0.050 $\mathrm{cm} .$ Find (a) the
volume of a single cookie and (b) the ratio of the diameter to the thickness, and express both in the proper number of significant figures.

Veronica P.
Numerade Educator

Problem 53

. Breathing oxygen. The density of air under standard laboratory conditions is $1.29 \mathrm{kg} / \mathrm{m}^{3},$ and about 20$\%$ of that air consists of oxygen. Typically, people breathe about $\frac{1}{2} \mathrm{L}$ of air per breath. (a) How many grams of oxygen does a person breathe in a day? (b) If this air is stored uncompressed in a cubical tank, how long is each side of the tank?

Bruce E.
Numerade Educator

Problem 54

$\bullet$ The total mass of Earth's atmosphere is about $5 \times 10^{15}$ metric tonnes $(1$ metric tonne $=1000 \mathrm{kg}) .$ Suppose you breathe in about 1$/ 3 \mathrm{L}$ of air with each breath, and the density of air at room temperature is about 1.2 $\mathrm{kg} / \mathrm{m}^{3} .$ About how
many breaths of air does the entire atmosphere contain? How does this compare to the number of atoms in one breath of air (about 1.2 $\times 10^{22} ) ?$ It's sometimes said that every breath you
take contains atoms that were also breathed by Albert Einstein, Confucius, and in fact anyone else who ever lived. Based on your calculation, could this be true?

Veronica P.
Numerade Educator

Problem 55

$\bullet$ How much blood in a heartbeat? A typical human contains 5.0 $\mathrm{L}$ of blood, and it takes 1.0 min for all of it to pass through the heart when the person is resting with a pulse rate
of 75 heartbeats per minute. On the average, what volume of blood, in liters and cubic centimeters, does the heart pump during each beat?

Bruce E.
Numerade Educator

Problem 56

. Muscle attachment. When muscles attach to bones, they usually do so by a series of tendons, as shown in Figure 1.27 In the figure, five tendons attach to the bone. The uppermost tendon pulls at $20.0^{\circ}$ from the axis of the bone, and each tendon is directed $10.0^{\circ}$ from the one next to it. (a) If each tendon exerts a 2.75 $\mathrm{N}$ pull on the bone, use vector components to find the magnitude and direction of the resultant force on this bone due to all five tendons. Let the axis of the bone be the $+x$ axis. (b) Draw a graphical sum to check your results from part (a).

Veronica P.
Numerade Educator

Problem 57

.. Hiking the Appalachian Trail. The Appalachian Trail runs from Mt. Katahdin in Maine to Springer Mountain in Georgia, a total distance of 2160 mi. If you hiked for 8 h per day, estimate (a) how many steps it would take to hike this trail and b) how many days it would take to hike it.

Bruce E.
Numerade Educator

Problem 58

. Estimate the number of atoms in your body. (Hint: Based on what you know about biology and chemistry, what are the most common types of atom in your body? What is the mass of each type of atom? Appendix $C$ gives the atomic masses for different elements, measured in atomic mass units; you can find the value of an atomic mass unit, or $1 \mathrm{u},$ in Appendix E.)

Veronica P.
Numerade Educator

Problem 59

$\bullet$ Biological tissues are typically made up of 98$\%$ water. Given that the density of water is $1.0 \times 10^{3} \mathrm{kg} / \mathrm{m}^{3},$ estimate the mass of (a) the heart of an adult human; (b) a cell with a diameter of $0.5 \mu \mathrm{m} ;$ (c) a honeybee.

Bruce E.
Numerade Educator

Problem 60

$\bullet$ Density of the human body. (a) Make simple measurements on your own body, and use them to calculate your body's average density (mass divided by volume) in $\mathrm{kg} / \mathrm{m}^{3}$ .
(b) How does this result compare with the density of water, which is 1000 $\mathrm{kg} / \mathrm{m}^{3} ?$ Is your result surprising?

Veronica P.
Numerade Educator

Problem 61

While surveying a cave, a spelunker follows a passage 180 $\mathrm{m}$ straight west, then 210 $\mathrm{m}$ in a direction $45^{\circ}$ east of south, and then 280 $\mathrm{m}$ at $30.0^{\circ}$ east of north. After a fourth unmeasured displacement, she finds herself back where she started. Use vector components to find the magnitude and direction of the fourth displacement. Then check the reasonableness of your answer with a graphical sum.

Bruce E.
Numerade Educator

Problem 62

$\bullet$ A sailor in a small sailboat encounters shifting winds. She sails 2.00 $\mathrm{km}$ east, then 3.50 $\mathrm{km}$ southeast, and then an additional distance in an unknown direction. Her final position is 5.80 $\mathrm{km}$ directly east of her starting point. (See Figure $1.28 . )$ Find the magnitude and direction of the third leg of the journey. Draw the vector addition diagram, and show that it in qualitative agreement with your numerical solution.

Veronica P.
Numerade Educator

Problem 63

$\bullet$ Dislocated shoulder. A patient with a dislocated shoulder is put into a traction apparatus as shown in Figure $1.29 .$ The pulls $\vec{A}$ and $\vec{B}$ have equal magnitudes and must combine to produce an outward traction force of 5.60 $\mathrm{N}$ on the patient's arm. How large should these pulls be?

Bruce E.
Numerade Educator

Problem 64

\bullet On a training flight, a student pilot flies from Lincoln, Nebraska to Clarinda, Iowa, then to St. Joseph, Missouri, and then to Manhattan, Kansas (Fig. 1.30). The directions are shown relative to
north: $0^{\circ}$ is north, $90^{\circ}$ is east, $180^{\circ}$ is south, and $270^{\circ}$ is west. Use the method of components to find (a) the distance she has to fly from Manhattan to get back to Lincoln, and (b) the direction (relative to north) she must fly to get there. Illustrate your solutions with a vector diagram.

Veronica P.
Numerade Educator

Problem 65

Bones and muscles. A patient in therapy has a forearm that weighs 20.5 $\mathrm{N}$ and lifts a 112.0 $\mathrm{N}$ weight. The only other significant forces on his forearm come from the biceps muscle
(which acts perpendicularly to the forearm) and the force at the elbow. If the biceps produce a pull of 232 $\mathrm{N}$ when the forearm is raised $43^{\circ}$ above the horizontal, find the magnitude and
direction of the force that the elbow exerts on the forearm. (Hint: The elbow force and the biceps force together must balance the weight of the arm and the weight it is carrying, so their vector sum must be 132.5 $\mathrm{N}$ upward.)

Bruce E.
Numerade Educator

Problem 66

$\bullet$ Googols and googolplexes! When the mathematician Edward Kasner asked his young nephew to coin a name for the huge number $10^{100}$ , the boy said googol. (a) Express the googol in standard notation as a 1 followed by the appropriate number of zeroes. (b) Approximately how many googols of atoms does our sun contain? For simplicity, assume that the sun consists of only protons and electrons, in equal numbers, which is approximately true. (Consult Appendix E.) (c) The googolplex is an even larger number, 10 to the googol power: $10^{\text { soogol. Express the googolplex in scientific notation. If you }}$ wrote it in standard notation with a 1 followed by the appropriate number of zeroes, how many zeroes would you need?

Veronica P.
Numerade Educator

Problem 67

What is total volume of the gas-exchanging region of the lungs?
A. 2000$\mu \mathrm{m}^{3}$
B. 2 $\mathrm{m}^{3}$
C. 2.0 $\mathrm{L}$
D. 120 $\mathrm{L}$

Bruce E.
Numerade Educator

Problem 68

Assuming the alveoli are spherical, what is the diameter of a typical alveolus?
A. 0.20 $\mathrm{mm}$
B. 2 $\mathrm{mm}$
C. 20 $\mathrm{mm}$
D. 200 $\mathrm{mm}$

Veronica P.
Numerade Educator

Problem 69

Individuals vary considerably in total lung volume. Figure 1.31 shows the results of measurement of total lung volume (horizontal axis) and average alveolar volume (vertical axis) for six individuals. What can you infer about the relationship between alveolar size, total lung volume and number of alveoli per individual from these data?
A. As the total volume of the lungs increases, the number and volume of individual alveoli increase.
B. As the total volume of the lungs increases, the number of alveoli increases and the volume of individual alveoli decreases.
C. As the total volume of the lungs increases, the volume of the individual alveoli remains constant and the number of alveoli increases.
D. As the total volume of the lungs increases, the number of alveoli and the volume of individual alveoli both remain constant.

Bruce E.
Numerade Educator