Physics Principles With Applications 7th Edition Giancoli Test Bank (With Instructor's Solution Manual)
INTRODUCTION, MEASUREMENT, ESTIMATING
1
1-2 Chap... [Show More] ter 1
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(a) There are about 800,000 people in San Francisco, as estimated in 2009 by the U.S. Census
Bureau. Assume that half of them have cars. If each of these 400,000 cars needs servicing twice
a year, then there are 800,000 visits to mechanics in a year. If mechanics typically work
50 weeks a year, then about 16,000 cars would need to be seen each week. Assume that on
average, a mechanic can work on 4 cars per day, or 20 cars a week. The final estimate, then, is
800 car mechanics in San Francisco.
(b) Answers will vary.
Responses to MisConceptual Questions
1. (d) One common misconception, as indicated by answers (b) and (c), is that digital measurements
are inherently very accurate. A digital scale is only as accurate as the last digit that it displays.
2. (a) The total number of digits present does not determine the accuracy, as the leading zeros in (c)
and (d) are only placeholders. Rewriting the measurements in scientific notation shows that (d)
has two-digit accuracy, (b) and (c) have three-digit accuracy, and (a) has four-digit accuracy.
Note that since the period is shown, the zeros to the right of the numbers are significant.
3. (b) The leading zeros are not significant. Rewriting this number in scientific notation shows that it
only has two significant digits.
4. (b) When you add or subtract numbers, the final answer should contain no more decimal places than
the number with the fewest decimal places. Since 25.2 has one decimal place, the answer must
be rounded to one decimal place, or to 26.6.
5. (b) The word “accuracy” is commonly misused by beginning students. If a student repeats a
measurement multiple times and obtains the same answer each time, it is often assumed to be
accurate. In fact, students are frequently given an “ideal” number of times to repeat the
experiment for “accuracy.” However, systematic errors may cause each measurement to be
inaccurate. A poorly working instrument may also limit the accuracy of your measurement.
6. (d) This addresses misconceptions about squared units and about which factor should be in the
numerator of the conversion. This error can be avoided when students treat the units as algebraic
symbols that must be cancelled out.
7. (e) When making estimates, students frequently believe that their answers are more significant than
they actually are. This question helps the student realize what an order-of-magnitude estimation
is NOT supposed to accomplish.
8. (d) This addresses the fact that the generic unit symbol, like [L], does not indicate a specific
system of units.
Solutions to Problems
1. (a) 214 3 significant figures
(b) 81 60 4 significant figures .
(c) 7 03 3 significant figures .
Introduction, Measurement, Estimating 1-3
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(d) 0 03 1 significant figure .
(e) 0 0086 2 significant figures .
(f) 3236 4 significant figures
(g) 8700 2 significant figures
2. (a) 0 1 156 1.156 10 .= ×
(b) 1 21.8 2.18 10 = ×
(c) 3 0.0068 6.8 10− = ×
(d) 2 328.65 3.2865 10 = ×
(e) 1 0.219 2.19 10− = ×
(f) 2 444 4.44 10 = ×
3. (a) 4 8.69 10 86,900 × =
(b) 3 9.1 10 9100 × =
(c) 1 8.8 10 0.88 − × =
(d) 2 4.76 10 476 × =
(e) 5 3.62 10 0.0000362 − × =
4. (a) 10 14 billion years 1.4 10 years = ×
(b)
7
10 17 3.156 10 s (1.4 10 yr) 4.4 10 s 1 yr
⎛ ⎞ ×
× = ⎜ ⎟ ×
⎝ ⎠
5. 0.25 m % uncertainty 100% 4.6% 5.48 m
= ×=
6. (a) 0.2 s % uncertainty 100% 3.636% 4% 5.5 s
=× = ≈
(b) 0.2 s % uncertainty 100% 3636% 0.4% 55 s
= × = 0. ≈
(c) The time of 5.5 minutes is 330 seconds.
0.2 s % uncertainty 100% 0.0606% 0.06% 330 s
=×= ≈
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7. To add values with significant figures, adjust all values to be added so that their exponents are all the
same.
3 4 6 3 33
3 35
(9.2 10 s) (8.3 10 s) (0.008 10 s) (9.2 10 s) (83 10 s) (8 10 s)
(9.2 83 8) 10 s 100.2 10 s 1.00 10 s
× + × + × = × + × +×
= + +× = × = ×
When you add, keep the least accurate value, so keep to the “ones” place in the last set of parentheses.
8. When you multiply, the result should have as many digits as the number with the least number of
significant digits used in the calculation.
2 1 22 (3.079 10 m)(0.068 10 m) 2.094 m 2.1 m − × ×= ≈
9. The uncertainty is taken to be 0.01 m.
2
2
0.01 m % uncertainty 100% 0.637% 1%
1.57 m
= ×= ≈
10. To find the approximate uncertainty in the volume, calculate the volume for the minimum radius and
the volume for the maximum radius. Subtract the extreme volumes. The uncertainty in the volume
is then half of this variation in volume.
4 4 3 33
specified specified 3 3 V r == = π π (0.84 m) 2.483 m
4 4 3 33
min min 3 3
4 4 3 33 max max 3 3
(0.80 m) 2.145 m
(0.88 m) 2.855 m
V r
V r
π π
π π
== =
== =
1 1 33 3
2 2 max min Δ= − = − = VVV ( ) (2.855 m 2.145 m ) 0.355 m
The percent uncertainty is
3
3
specified
0.355 m 100 14.3 14% .
2.483 m
V
V
Δ
= ×= ≈
11. To find the approximate uncertainty in the area, calculate the area for the specified radius, the
minimum radius, and the maximum radius. Subtract the extreme areas. The uncertainty in the area
is then half this variation in area. The uncertainty in the radius is assumed to be 4 0.1 10 cm. ×
2 4 2 9 2
specified specified A r = =× =× π π (3.1 10 cm) 3.019 10 cm
2 4 2 9 2
min min A r ==× =× π π (3.0 10 cm) 2.827 10 cm
2 4 2 9 2 max max A r = =× =× π π (3.2 10 cm) 3.217 10 cm
1 1 92 92 9 2
2 2 max min Δ= − = × − × = × AA A ( ) (3.217 10 cm 2.827 10 cm ) 0.195 10 cm
Thus the area should be quoted as 9 2 A =±× (3.0 0.2) 10 cm .
12. (a) 286.6 mm 3 286.6 10 m − × 0.2866 m
(b) 85 Vμ 6 85 10 V − × 0.000085 V
(c) 760 mg 6 760 10 kg − × 0.00076 kg (if last zero is not significant)
Introduction, Measurement, Estimating 1-5
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(d) 62.1 ps 12 62.1 10 s − × 0.0000000000621 s
(e) 22.5 nm 9 22.5 10 m − × 0.0000000225 m
(f) 2.50 gigavolts 9 2.50 10 volts × 2,500,000,000 volts
Note that in part (f ) in particular, the correct number of significant digits cannot be determined when
you write the number in this format.
13. (a) 6 1 10 volts × 1 megavolt 1 MV =
(b) 6 2 10 meters − × 2 micrometers 2 m = μ
(c) 3 6 10 days × 6 kilodays 6 kdays =
(d) 2 18 10 bucks × 18 hectobucks 18 hbucks = or 1.8 kilobucks
(e) 7 7 10 seconds − × 700 nanoseconds 700 ns or 0.7 s = μ
14.
2 4 2
4 2
1.000 10 m 3.281 ft 1 acre 1 hectare (1 hectare) 2.471 acres 1 hectare 1 m 4.356 10 ft
⎛ ⎞ × ⎛ ⎞ ⎛ ⎞ = = ⎜ ⎟⎜ ⎟ ⎜ ⎟
⎝ ⎠⎝ ⎠ ⎝ ⎠ ×
15. (a) 6 11 93 million miles (93 10 miles)(1610 m/1 mile) 1.5 10 m =× =×
(b) 11 11 3 8 1.5 10 m (1.5 10 m)(1 km/10 m) 1.5 10 km × = × =×
16. To add values with significant figures, adjust all values to be added so that their units are all the same.
5 1.80 m 142.5 cm 5.34 10 m 1.80 m 1.425 m 0.534 m 3.759 m 3.76 m + +× = + + = = μ
When you add, the final result is to be no more accurate than the least accurate number used. In this
case, that is the first measurement, which is accurate to the hundredths place when expressed in meters.
17. (a) 10 10 9 1.0 10 m 1.0 10 m 39.37 in/1 m 3.9 10 in − − − × = ( × )( ) = ×
(b) 8
10
1 m 1 atom (1.0 cm) 1.0 10 atoms
100 cm 1.0 10 m −
⎛ ⎞⎛ ⎞
⎜ ⎟⎜ ⎟ = ×
⎝ ⎠⎝ ⎠ ×
18. (a) 0.621 mi (1 km/h) 0.621 mi/h, 1 km
⎛ ⎞ ⎜ ⎟ =
⎝ ⎠
so the conversion factor is 0.621 mi/h . 1 km/h
(b) 3.28 ft (1 m/s) 3.28 ft/s, 1 m
⎛ ⎞ ⎜ ⎟ =
⎝ ⎠
so the conversion factor is 3.28 ft/s . 1 m/s
(c) 1000 m 1 h (1 km/h) 0.278 m/s, 1 km 3600 s
⎛ ⎞⎛ ⎞ ⎜ ⎟⎜ ⎟ =
⎝ ⎠⎝ ⎠
so the conversion factor is 0.278 m/s . 1 km/h
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Note that if more significant figures were used in the original factors, such as 0.6214 miles per
kilometer, more significant figures could have been included in the answers.
19. (a) Find the distance by multiplying the speed by the time.
8 7 15 15 1.00 ly (2.998 10 m/s)(3.156 10 s) 9.462 10 m 9.46 10 m = × × = × ≈×
(b) Do a unit conversion from ly to AU.
15
4
11
9.462 10 m 1 AU (1.00 ly) 6.31 10 AU
1.00 ly 1.50 10 m
⎛ ⎞ × ⎛ ⎞ ⎜ ⎟⎜ ⎟ = ×
⎝ ⎠⎝ ⎠ ×
20. One mile is 1609 m, according to the unit conversions in the front of the textbook. Thus it is 109 m
longer than a 1500-m race. The percentage difference is calculated here.
109 m 100% 7.3%
1500 m
× =
21. Since the meter is longer than the yard, the soccer field is longer than the football field.
soccer football
1.094 yd 100.0 m 100.0 yd 9.4 yd 1 m
A A −= × − =
soccer football
1 m 100.0 m 100.0 yd 8.6 m 1.094 yd
A A −= − × =
Since the soccer field is 109.4 yd compared with the 100.0-yd football field, the soccer field
is 9.4% longer than the football field.
22. (a) # of seconds in 1.00 yr:
7 3.156 10 s 7 1.00 yr (1.00 yr) 3.16 10 s 1 yr
⎛ ⎞ ×
= =× ⎜ ⎟
⎝ ⎠
(b) # of nanoseconds in 1.00 yr:
7 9 3.156 10 s 1 10 ns 16 1.00 yr (1.00 yr) 3.16 10 ns 1 yr 1 s
⎛ ⎞ × × ⎛ ⎞ = = ⎜ ⎟⎜ ⎟ ×
⎝ ⎠⎝ ⎠
(c) # of years in 1.00 s: 8
7
1 yr 1.00 s 1.00 s 3.17 10 yr
3.156 10 s
− ⎛ ⎞
=( ) = × ⎜ ⎟
⎝ ⎠ ×
23. (a)
15
12
27
10 kg 1 proton or neutron 10 protons or neutrons 1 bacterium 10 kg
−
−
⎛ ⎞⎛ ⎞ ⎜ ⎟⎜ ⎟ =
⎝ ⎠⎝ ⎠
(b)
17
10
27
10 kg 1 proton or neutron 10 protons or neutrons 1 DNA molecule 10 kg
−
−
⎛ ⎞⎛ ⎞ ⎜ ⎟⎜ ⎟ = ⎜ ⎟ ⎝ ⎠⎝ ⎠
(c)
2
29
27
10 kg 1 proton or neutron 10 protons or neutrons 1 human 10 kg −
⎛ ⎞⎛ ⎞ ⎜ ⎟⎜ ⎟ =
⎝ ⎠⎝ ⎠
(d)
41
68
27
10 kg 1 proton or neutron 10 protons or neutrons 1 Galaxy 10 kg −
⎛ ⎞⎛ ⎞ ⎜ ⎟⎜ ⎟ =
⎝ ⎠⎝ ⎠
Introduction, Measurement, Estimating 1-7
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24. The radius of the ball can be found from the circumference (represented by “c” in the equations
below), and then the volume can be found from the radius. Finally, the mass is found from the volume
of the baseball multiplied by the density ( mass/volume) ρ = of a nucleon.
( )
3
ball ball 4 4 3
ball ball ball ball ball 3 3
nucleon nucleon nucleon
ball ball nucleon ball ball ball 4 3 3 4 1 nucleon 3 nucleon 3 2 nucleon
2
4 ball n
3
2 ; 2 2
2
c c c rr V r
mm m mV V V V
V r d
c m
π π π
π π
ρ
π π
π
π
⎛ ⎞ = →= = = ⎜ ⎟ ⎝ ⎠
⎛ ⎞ ⎛ ⎞ ⎛ ⎞ ⎜ ⎟ == = = ⎜ ⎟ ⎜ ⎟ ⎜ ⎟ ⎜ ⎟ ⎝ ⎠ ⎝ ⎠ ⎝ ⎠
⎛ ⎞ = ⎜ ⎟ ⎝ ⎠ ( )
3 3
ucleon ball 27
nucleon 3 15 4 1 nucleon
3 2 nucleon
14 14
0.23 m (10 kg)
(10 m)
3.9 10 kg 4 10 kg
c
m
d d π π π
−
−
⎛ ⎞ ⎛ ⎞ ⎛ ⎞ ⎜ ⎟ = = ⎜ ⎟ ⎜ ⎟ ⎜ ⎟ ⎝ ⎠ ⎝ ⎠ ⎝ ⎠
= × ≈×
25. (a) 3 33 2800 2.8 10 1 10 10 = × ≈× =
(b) 3 4 45 86.30 10 8.630 10 10 10 10 × = × ≈× =
(c) 3 32 0.0076 7.6 10 10 10 10 − −− = × ≈× =
(d) 8 9 99 15 0 10 1 5 10 1 10 10 .× =.× ≈× =
26. The textbook is approximately 25 cm deep and 5 cm wide. With books on both sides of a shelf, the
shelf would need to be about 50 cm deep. If the aisle is 1.5 m wide, then about 1/4 of the floor space is
covered by shelving. The number of books on a single shelf level is then
1 2 4
4
1 book (3500 m ) 7.0 10 books. (0.25 m)(0.05 m)
⎛ ⎞ ⎜ ⎟ = ×
⎝ ⎠
With 8 shelves of books, the total number of books
stored is as follows:
( ) 4 5 books 7 0 10 8 shelves 6 10 books
shelf level
⎛ ⎞ .× ≈ × ⎜ ⎟ ⎝ ⎠
27. The distance across the U.S. is about 3000 miles.
(3000 mi)(1 km/0.621 mi)(1 h/10 km) 500 h ≈
Of course, it would take more time on the clock for a runner to run across the U.S. The runner
obviously could not run for 500 hours non-stop. If he or she could run for 5 hours a day, then it would
take about 100 days to cross the country.
28. A commonly accepted measure is that a person should drink eight 8-oz. glasses of water each day.
That is about 2 quarts, or 2 liters of water per day. Approximate the lifetime as 70 years.
4 (70 yr)(365 d/1 yr)(2 L/1 d) 5 10 L ≈ ×
29. An NCAA-regulation football field is 360 feet long (including the end zones) and 160 feet wide,
which is about 110 meters by 50 meters, or 2 5500 m . We assume the mower has a cutting width of
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0.5 meters and that a person mowing can walk at about 4.5 km/h, which is about 3 mi/h. Thus the
distance to be walked is as follows:
2 area 5500 m 11000 m 11 km
width 0.5 m
d == = =
At a speed of 4.5 km/h, it will take about 1 h 11 km 2.5 h
4.5 km
× ≈ to mow the field.
30. There are about 8 3 10 × people in the U.S. Assume that half of them have cars, that they drive an
average of 12,000 miles per year, and that their cars get an average of 20 miles per gallon of gasoline.
8 1 automobile 12,000 mi/auto 1 gallon 11 (3 10 people) 1 10 gal/yr 2 people 1 yr 20 mi
⎛ ⎞⎛ ⎞⎛ ⎞
× ≈ ⎜ ⎟⎜ ⎟⎜ ⎟ ×
⎝ ⎠⎝ ⎠⎝ ⎠
31. In estimating the number of dentists, the assumptions and estimates needed are:
• the population of the city
• the number of patients that a dentist sees in a day
• the number of days that a dentist works in a year
• the number of times that each person visits the dentist each year
We estimate that a dentist can see 10 patients a day, that a dentist works 225 days a year, and that each
person visits the dentist twice per year.
(a) For San Francisco, the population as of 2010 was about 800,000 (according to the U.S. Census
Bureau). The number of dentists is found by the following calculation:
5 2 visits/yr 1 yr 1 dentist (8 10 people) 700 dentists
1 person 225 workdays 10 visits/workday
⎛ ⎞⎛ ⎞⎛ ⎞
× ≈ ⎜ ⎟⎜ ⎟⎜ ⎟ ⎝ ⎠⎝ ⎠⎝ ⎠
(b) For Marion, Indiana, the population is about 30,000. The number of dentists is found by a
calculation similar to that in part (a), and would be about 30 dentists . There are about 40
dentists (of all types, including oral surgeons and orthodontists) listed in the 2012 Yellow Pages.
32. Consider the diagram shown (not to scale). The balloon is a distance h = 200 m
above the surface of the Earth, and the tangent line from the balloon height to the
surface of the Earth indicates the location of the horizon, a distance d away from
the balloon. Use the Pythagorean theorem.
( )
222 2 222
2 2 2
6 4 2 4
() 2
2 2
2(6.4 10 m)(200 m) 200 m 5.1 10 m 5 10 m ( 80 mi)
r h r d r rh h r d
rh h d d rh h
d
+ =+ → + +=+
+= →= +
= × + = × ≈× ≈
33. At $1,000 per day, you would earn $30,000 in the 30 days. With the other pay method, you would
get 1 $0.01(2 ) t− on the tth day. On the first day, you get 1 1 $0.01(2 ) $0.01. − = On the second day,
you get 2 1 $0.01(2 ) $0.02. − = On the third day, you get 3 1 $0.01(2 ) $0.04. − = On the 30th day, you
get 30 1 6 $0.01(2 ) $5.4 10 , − = × which is over 5 million dollars. Get paid by the second method.
h
r
r
d
Introduction, Measurement, Estimating 1-9
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To 1st sunset
To 2nd sunset
A
B
Earth center
R
R
d h
θ
θ
34. In the figure in the textbook, the distance d is perpendicular to the radius that is drawn approximately
vertically. Thus there is a right triangle, with legs of d and R, and a hypotenuse of R h + . Since
2 h R h Rh , 2.
2
22 2 2 2 2 2 2
2
6
() 2 2 2
2
(4400 m) 6.5 10 m
2(1.5 m)
d d R R h R Rh h d Rh h d Rh R
h
+=+ =+ + = + ≈ = → →→
= =×
A better measurement gives 6 R = × 6.38 10 m.
35. For you to see the Sun “disappear,” your line of sight
to the top of the Sun must be tangent to the Earth’s
surface. Initially, you are lying down at point A, and
you see the first sunset. Then you stand up, elevating
your eyes by the height h = 130 cm. While you stand,
your line of sight is tangent to the Earth’s surface at
point B, so that is the direction to the second sunset.
The angle θ is the angle through which the Sun
appears to move relative to the Earth during the time
to be measured. The distance d is the distance from
your eyes when standing to point B.
Use the Pythagorean theorem for the following relationship:
22 2 2 2 2 2 d R R h R Rh h d Rh h + =+ = + + → = + () 2 2
The distance h is much smaller than the distance R, so 2 h Rh 2 which leads to 2 d Rh ≈ 2 . We also
have from the same triangle that d R/ tan , = θ so d R = tan . θ Combining these two relationships gives
2 22 d Rh R ≈ = 2 tan , θ so 2
2 . tan
h R
θ =
The angle θ can be found from the height change and the radius of the Earth. The elapsed time
between the two sightings can then be found from the angle, because we know that a full revolution
takes 24 hours.
1 1 2 o
2 6
o
2 o
o o
2 2 2(1.3 m) tan tan (3 66 10 )
tan 6.38 10 m
sec 3600 s 360 24 h
1 h
3600 s (3 66 10 ) 3600 s 24 h 24 h 8.8 s
360 1 h 360 1 h
h h R
R
t
t
θ
θ
θ
θ
− − −
−
= → = = =.×
×
= →
×
⎛ ⎞⎛⎞ ⎛⎞ ⎛ ⎞ . ×
= ×= ×= ⎜⎟ ⎜⎟ ⎜ ⎟ ⎜ ⎟ ⎝ ⎠⎝⎠ ⎝⎠ ⎝ ⎠
36. 3
mass units Density units volume units
M
L
⎡ ⎤ = = ⎢ ⎥ ⎣ ⎦
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37. (a) For the equation 3 υ = − At Bt, the units of 3 At must be the same as the units of . υ So the units
of A must be the same as the units of 3 υ/ , t which would be 4 L T/ . Also, the units of Bt must be
the same as the units of . υ So the units of B must be the same as the units of υ/ ,t which would
be 2 L T/ .
(b) For A, the SI units would be 4 m/s , and for B, the SI units would be 2 m/s .
38. (a) The quantity 2 υt has units of 2 (m/s)(s ) m s, = i which do not match with the units of meters for x.
The quantity 2at has units 2 (m/s )(s) m/s, = which also do not match with the units of meters for x.
Thus this equation cannot be correct .
(b) The quantity 0 υ t has units of (m/s)(s) m, = and 1 2
2 at has units of 2 2 (m/s )(s ) m. = Thus, since
each term has units of meters, this equation can be correct .
(c) The quantity 0 υ t has units of (m/s)(s) m, = and 2 2at has units of 2 2 (m/s )(s ) m. = Thus, since
each term has units of meters, this equation can be correct .
39. Using the units on each of the fundamental constants (c, G, and h), we find the dimensions of the
Planck length. We use the values given for the fundamental constants to find the value of the Planck
length.
[ ]
3 2 2 32 3 5
2
3 3 33 3
[ / ][ / ] [/] P
Gh L MT ML T L L T M L L L
c L T MT L L
⎡ ⎤ ⎡⎤
=→ = === ⎡ ⎤ ⎢ ⎥ ⎢⎥ ⎣ ⎦ ⎣ ⎦ ⎣⎦
A
11 3 2 34 2
35
3 8 3
(6.67 10 m /kg s )(6.63 10 kg m /s) 4 05 10 m
(3.00 10 m/s) P
Gh
c
− − × × − = = =. ×
×
i i A
Thus the order of magnitude is 35 10 m . −
40. The percentage accuracy is 5
7
2 m 100% 1 10 % .
2 10 m
− × =×
×
The distance of 20,000,000 m needs to be
distinguishable from 20,000,002 m, which means that 8 significant figures are needed in the distance
measurements.
41. Multiply the number of chips per wafer by the number of wafers that can be made from a cylinder.
We assume the number of chips per wafer is more accurate than 1 significant figure.
chips 1 wafer 250 mm 5 chips 400 3.3 10
wafer 0.300 mm 1 cylinder cylinder
⎛ ⎞⎛ ⎞⎛ ⎞ ⎜ ⎟⎜ ⎟ = × ⎜ ⎟ ⎝ ⎠⎝ ⎠⎝ ⎠
42. Assume that the alveoli are spherical and that the volume of a typical human lung is about 2 liters,
which is 3 0.002 m . The diameter can be found from the volume of a sphere, 4 3
3 π r .
Introduction, Measurement, Estimating 1-11
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3
4 4 3 3
3 3
1 3 3 3
8 33 3 4
8
( /2) 6
6(2 10 ) (3 10 ) 2 10 m m 2 10 m 6 3 10
/
d r d
d d
π
π π
π
π
− − −
= =
⎡ ⎤ ×
× =× → = = × ⎢ ⎥ ⎢ ⎥ ⎣ ⎦ ×
43. We assume that there are 40 hours of work per week and that the typist works 50 weeks out of the
year.
12 1 char 1 min 1 hour 1 week 1 year 4 (1.0 10 bytes) 4.629 10 years 1 byte 180 char 60 min 40 hour 50 weeks
46,000 years
× × × × × × =×
≈
44. The volume of water used by the people can be calculated as follows:
3 3
4 3 3
5
1200 L/day 365 days 1000 cm 1 km (4 10 people) 4.38 10 km /yr 4 people 1 yr 1 L 10 cm
− ⎛ ⎞⎛ ⎞⎛ ⎞⎛ ⎞
× = ⎜ ⎟⎜ ⎟⎜ ⎟⎜ ⎟ × ⎜ ⎟⎜ ⎟ ⎝ ⎠⎝ ⎠⎝ ⎠⎝ ⎠
The depth of water is found by dividing the volume by the area.
3 3 5
5
2
4.38 10 km /yr km 10 cm 8.76 10 8.76 cm/yr 9 cm/yr
50 km yr 1 km
V d
A
− − × ⎛ ⎞⎛ ⎞
== = × = ≈ ⎜ ⎟⎜ ⎟ ⎝ ⎠⎝ ⎠
45. We approximate the jar as a cylinder with a uniform cross-sectional area. In counting the jelly beans
in the top layer, we find about 25 jelly beans. Thus we estimate that one layer contains about 25 jelly
beans. In counting vertically, we see that there are about 15 rows. Thus we estimate that there
are 25 15 375 400 jelly beans ×= ≈ in the jar.
46. The volume of a sphere is given by 4 3
3 V r = π , so the radius is
1/3 3 . 4
V r π
⎛ ⎞ = ⎜ ⎟ ⎝ ⎠ For a 1-ton rock, the
volume is calculated from the density, and then the diameter from the volume.
3 2000 lb 1 ft 3 (1 T) 10.8 ft 1 T 186 lb
V ⎛ ⎞⎛ ⎞ = = ⎜ ⎟⎜ ⎟ ⎜ ⎟ ⎝ ⎠⎝ ⎠
1/3 1/3 3 3 3(10.8 ft ) 2 2 2 2.74 ft 3 ft
4 4
V d r
π π
⎡ ⎤ ⎛ ⎞ == = = ≈ ⎜ ⎟ ⎢ ⎥ ⎝ ⎠ ⎢ ⎥ ⎣ ⎦
47. We do a “units conversion” from bytes to minutes, using the given CD reading rate.
6
6
8 bits 1 s 1 min (783.216 10 bytes) 74.592 min 75 min 1 byte 60 s 1.4 10 bits
× ×× ×= ≈
×
48. A pencil has a diameter of about 0.7 cm. If held about 0.75 m from the eye, it can just block out the
Moon. The ratio of pencil diameter to arm length is the same as the ratio of Moon diameter to Moon
distance. From the diagram, we have the following ratios. [Show Less]