Chapter 19 Solutions

Size: px

Start display at page:

Download "Chapter 19 Solutions"

Damian Collins
5 years ago
Views:

1 Chapter 19 Solutions *19.1 (a) To convert from Fahrenheit to Celsius, we use T C = 5 9 (T F 32.0) = 5 ( ) = 37.0 C 9 and the Kelvin temperature is found as T = T C = 310 K In a fashion identical to that used in (a), we find T C = 20.6 C and T = 253 K 19.2 P 1 V = nrt 1 and P 2 V = nrt 2 imply that P 2 P 1 = T 2 T 1 (a) P 2 = P 1T 2 T 1 = (0.980 atm)( )K ( )K = 1.06 atm T 3 = T 1P 3 P 1 = (293 K)(0.500 atm) (0.980 atm) = 149 K = 124 C 19.3 Since we have a linear graph, the pressure is related to the temperature as P = A + BT, where A and B are constants. To find A and B, we use the data atm = A + ( 80.0 C)B (1) atm = A + (78.0 C)B (2) Solving (1) and (2) simultaneously, we find A = atm and B = atm/ C Therefore, P = atm + ( atm/ C)T (a) At absolute zero P = 0 = atm + ( atm/ C)T which gives T = 274 C

2 2 Chapter 19 Solutions At the freezing point of water P = atm + 0 = 1.27 atm (c) and at the boiling point P = atm + ( atm/ C)(100 C) = 1.74 atm 19.4 Let us use T C = 5 9 (T F 32.0) with T F = 40.0 C. We find T C = 5 ( ) = 40.0 C (a) T F = 9 5 T C F = 9 ( ) = 320 F 5 T = T C = = 77.3 K 19.6 Require 0.00 C = a( 15.0 S) + b 100 C = a(60.0 S) + b Subtracting, 100 C = a(75.0 S) a = 1.33 C /S Then 0.00 C = 1.33( 15.0 S)C + b b = 20.0 C So the conversion is T C = (1.33 C /S )T S C 19.7 (a) T = 450 C = 450 C 212 F 32.0 F 100 C 0.00 C = 810 F T = 450 C = 450 K 19.8 (a) T = = 1337 K melting point T = = 2933 K boiling point T = 1596 C = 1596 K The differences are the same.

3 Chapter 19 Solutions The wire is 35.0 m long when T C = 20.0 C L = L i α (T T i ) α α(20.0 C) = (C ) 1 for Cu. L = (35.0 m)( (C ) 1 ( 35.0 C ( 20.0 C)) = cm Goal Solution G: Based on everyday observations of telephone wires, we might expect the wire to expand by less than a meter since the change in length of these wires is generally not noticeable. O: The change in length can be found from the linear expansion of copper wire (we will assume that the insulation around the copper wire can stretch more easily than the wire itself). From Table 19.2, the coefficient of linear expansion for copper is ( C) 1. A: The change in length between cold and hot conditions is L = αl 0 T = [ ( C) 1 ](35.0 m)(35.0 C ( 20.0 C)) L = m or L = 3.27 cm L: This expansion is well under our expected limit of a meter. From L, we can find that the wire sags m at its midpoint on the hot summer day, which also seems reasonable based on everyday observations L = L i α T = (25.0 m)( /C )(40.0 C ) = 1.20 cm (a) L = αl i T = (C ) -1 ( m)(80.0 C) = m Lf = m L = (C ) -1 ( m)( 20.0 C) = L f = m (a) L Al (1 + α Al T) = L Brass (1 + α Brass T) T = L Al L Brass L Brass α Brass L Al α Al T = ( ) (10.00)( ) (10.01)( ) T = 199 C so T = 179 C This is attainable.

4 4 Chapter 19 Solutions T = ( ) (10.00)( ) (10.02)( ) T = 396 C so T = 376 C which is below 0 K so it cannot be reached For the dimensions to increase, L = αl i T cm = ( / C)(2.20 cm)(t 20.0 C) T = 55.0 C α = deg 1 for steel L = (518 m)( deg 1 )[ 35.0 C ( 20.0 C)] = m *19.15 (a) A = 2αA i ( T) A = 2( / C)( m) 2 (50.0 C) A = m 2 = cm 2 The length of each side of the hole has increased. Thus, this represents an increase in the area of the hole V = (β 3α)V i T = [( ( )](50.0 gal)(20.0) = gal (a) L = αl i T = (C ) 1 (30.0 cm)(65.0 C) = mm L = (C ) 1 (1.50 cm)(65.0 C) = cm (c) V = 3αV i T = 3( / C) (30.0)(π)(1.50)2 4 cm 3 (65.0 C) = cm 3

5 Chapter 19 Solutions (a) V f = V i (1 + β T) = 100[ ( 15.0)] = 99.8 ml V acetone = (βv i T) acetone V flask = (βv i T) Pyrex = (3αV i T) Pyrex for same V i, T, V acetone V flask = β acetone = 4 β flask 3( ) = The volume change of flask is about 6% of the change in the acetone's volume (a) and The material would expand by L = αl i T, L L i = α T, but instead feels stress F A = Y L L i = Yα T = ( N/m 2 ) (C ) 1 (30.0 C ) = N/m 2 This will not break concrete (a) and The gap width is a linear dimension, so it increases in "thermal enlargement" by L = αl i T = ( /C )(1.60 cm)(160 C ) = cm so L f = cm In F A = Y L L i require L = αl i T F A = Yα T F T = AYα = 500 N ( m 2 )( N/m 2 )( /C ) T = 1.14 C

6 6 Chapter 19 Solutions L = αl i ( T) and F A = Y L L i F = AY L L i = AYα ( T) = π( m) N m 2 ( /C )(70.0 C) F = 199 kn (a) V = V t β t T V Al β Al T = (β t 3α Al )V i T = ( )( C) 1 (2000 cm 3 )(60.0 C) V = 99.4 cm 3 overflows The whole new volume of turpentine is 2000 cm 3 + ( / C)(2000 cm 3 )(60.0 C) = 2108 cm 3 so the fraction lost is 99.4 cm cm3 = and this fraction of the cylinder's depth will be empty upon cooling: ( )(20.0 cm) = cm (a) L = L i (1 + α T) cm = (5.000 cm) [ C 1 (T 20.0 C)] T = 437 C We must get L Al = L Brass for some T, or L i,al (1 + α Al T) = L i,brass (1 + α brass T) (5.000 cm)[1 + ( C 1 ) T] = (5.050 cm)[1 + ( C 1 ) T] Solving for T gives T = 2080 C, so T = 3000 C This will not work because aluminum melts at 660 C *19.25 (a) n = PV RT = (9.00 atm)( Pa/atm)( m 3 ) (8.315 N mol K)(293 K) = 3.00 mol N = nn A = (3.00 mol)( molecules/mol) = molecules

7 Chapter 19 Solutions PV = NP'V' = 4 3 π r 3 NP' N = 3PV 4π r 3 P' = (3)(150)(0.100) (4π )(0.150) 3 (1.20) ( )(6000) = n(8.315)(293) n = mol = 884 balloons N = molecules Goal Solution G: The given room conditions are close to Standard Temperature and Pressure (STP is 0 C and kpa), so we can use the estimate that one mole of an ideal gas at STP occupies a volume of about 22 L. The volume of the auditorium is 6000 m 3 and 1 m 3 = 1000 L, so we can estimate the number of molecules to be: N ( m 3 ) 1000 L 1 mol 1 m 3 22 L molecules 1 mol molecules of air O: The number of molecules can be found more precisely by applying PV = nrt. A: The equation of state of an ideal gas is PV = nrt so we need to solve for the number of moles to find N. n = PV RT = ( N/m 2 )[(10.0 m)(20.0 m)(30.0 m)] (8.315 J/mol K)(293 K) = mol N = n(n A ) = ( mol) molecules mol = molecules L: This result agrees quite well with our initial estimate. The numbers would match even better if the temperature of the auditorium was 0 C P = nrt V = 9.00 g J 18.0 g/mol 773 K mol K m3 = 1.61 MPa = 15.9 atm

8 8 Chapter 19 Solutions ρ out gv ρ in gv (200 kg)g = 0 (ρ out ρ in )(400 m 3 ) = 200 kg 1.25 kg m K (400 m T 3 ) = 200 kg in T in = = 283 T in T in = 472 K Goal Solution G: The air inside the balloon must be significantly hotter than the outside air in order for the balloon to have a net upward force, but the temperature must also be less than the melting point of the nylon used for the balloon s envelope (rip-stop nylon melts around 200 C), otherwise the results could be disastrous! O: The density of the air inside the balloon must be sufficiently low so that the buoyant force is greater than the weight of the balloon, its cargo, and the air inside. The temperature of the air required to achieve this density can be found from the equation of state of an ideal gas. B F g F g of 200 kg of air A: The buoyant force equals the weight of the air at 10.0 C displaced by the balloon: B = m air g = ρ a Vg = (1.25 kg/m 3 )(400 m 3 )(9.8 m/s 2 ) = 4900 N The weight of the balloon and its cargo is F g = m b g = (200 kg)(9.80 m/s 2 ) = 1960 N Since B > F g, the balloon has a chance of lifting off as long as the weight of the air inside the balloon is less than the difference in these forces: F g(air) < B F g(balloon) = 4900 N 1960 N = 2940 N The mass of this air is m air = F g(air) g = 2940 N 9.80 m/s2 = 300 kg

9 Chapter 19 Solutions 9 To find the required temperature of this air from PV = nrt, we must find the corresponding number of moles of air. Dry air is approximately 20% O 2, and 80% N 2. Using data from a periodic table, we can calculate the molar mass of the air to be approximately M = 0.80(28 g/mol) (32 g/mol) = 29 g/mol so the number of moles is n = m 300 kg = 10 3 g M 29 g/mol 1 kg = mol The pressure of this air is the ambient pressure; from PV= nrt, we can now find the minimum temperature required for lift off: T = PV nr = ( N/m 2 )(400 m 3 ) ( mol)(8.315 J/(mol K)) = 471 K = 198 C L: The average temperature of the air inside the balloon required for lift off appears to be close to the melting point of the nylon fabric, so this seems like a dangerous situation! A larger balloon would be better suited for the given weight of the balloon. (A quick check on the internet reveals that this balloon is only about 1/10 the size of most sport balloons, which have a volume of about 3000 m 3 ). If the buoyant force were less than the weight of the balloon and its cargo, the balloon would not lift off no matter how hot the air inside might be! If this were the case, then either the weight would have to be reduced or a bigger balloon would be required. Even though our result for T is shown with 3 significant figures, the answer should probably be rounded to 2 significant figures to reflect the approximate value of the molar mass of the air. *19.30 (a) T 2 = T 1 P 2 P 1 = (300 K)(3) = 900 K T 2 = T 1 P 2 V 2 P 1 V 1 = 300(2)(2) = 1200 K *19.31 (a) PV = nrt n = PV RT = ( Pa)(1.00 m 3 ) = 41.6 mol (8.315 J/mol K)(293 K) m = nm = (41.6 mol)(28.9 g/mol) = 1.20 kg, in agreement with the tabulated density of 1.20 kg/m 3 at 20.0 C. *19.32 (a) PV = nrt n = PV RT m = nm = PVM RT = ( Pa)(0.100 m) 3 ( kg/mol) (8.315 J/mol K)(300 K) m = kg F g = mg = ( kg)(9.80 m/s 2 ) = 11.5 mn

10 10 Chapter 19 Solutions (c) (d) F = PA = ( N/m 2 )(0.100 m) 2 = 1.01 kn The molecules must be moving very fast to hit the walls hard (a) Initially, P i V i = n i RT i (1.00 atm)v i = n i R( )K Finally, P f V f = n f RT f P f (0.280V i ) = n i R( )K Dividing these equations, P f 1.00 atm = K K giving P f = 3.95 atm or P f = Pa(abs.) After being driven P d (1.02)(0.280V i ) = n i R( )K P d = 1.121P f = Pa *19.34 Let us use V = 4 3 π r 3 as the volume of the balloon, and the ideal gas law in the form P f V f T f = P i V i T i to give, r 3 i = 300 K 200 K r i = 7.11 m atm (20.0 m) atm P 1 V 1 = n 1 RT 1 P 2 V 2 = n 2 RT 2 n 1 n 2 = PV RT 1 PV RT 2 n 1 n 2 = ( Pa)80.0 m J/mol K 291 K K n 1 n 2 = 78.4 mol m = nm = 78.4 mol(28.9 g/mol) = 2.27 kg

11 Chapter 19 Solutions P 0 V = n 1 RT 1 = (m 1 /M)RT 1 P 0 V = n 2 RT 2 = (m 2 /M)RT 2 m 1 m 2 = P 0VM R 1 1 T 1 T At depth, P = P 0 + ρgh and PV i = nrt i at the surface, P 0 V f = nrt f P 0 V f (P 0 + ρgh)v i = T f T i V f = V T f P 0 + ρgh i T i P 0 V f = 1.00 cm K Pa kg/m 3 (9.80 m/s 2 )25.0 m 278 K Pa V f = 3.67 cm 3 *19.38 My bedroom is 4.00 m long, 4.00 m wide, and 2.40 m high, enclosing air at 100 kpa and 20.0 C = 293 K. Think of the air as 80.0% N 2 and 20.0% O 2. Avogadro's number of molecules has mass g/mol g/mol = kg/mol Then PV = nrt = (m/m)rt gives m = PVM RT = ( N/m 2 )(38.4 m 3 )( kg/mol) (8.315 J/mol K)(293 K) m = 45.4 kg ~ 10 2 kg PV = nrt m f = n f = P fv f RT i = P f, so m m i n i RT f P i V i P f = m i P f i P i m = m i m f = m i P i P f P i = (12.0 kg) 41.0 atm 26.0 atm = 4.39 kg 41.0 atm

12 12 Chapter 19 Solutions N = PVN A RT (10 9 Pa)(1.00 m 3 )( ) molecule mol = = molecules J (300 K) K mol PV = nrt V = nrt P (1.00 mol)(8.315 J/mol K)(273 K) = 10 3 L N/m m 3 = 22.4 L (a) Initially the air in the bell satisfies P 0 V bell = nrt i or P 0 [(2.50 m)a] = nrt i (1) When the bell is lowered, the air in the bell satisfies P bell (2.50 m x)a = nrt f (2) where x is the height the water rises in the bell. Also, the pressure in the bell, once it is lowered, is equal to the sea water pressure at the depth of the water level in the bell. P bell = P 0 + ρg (82.3 m x) P 0 + ρg(82.3 m) (3) The approximation is good, as x < 2.50 m. Substituting (3) into (2) and substituting nr from (1) into (2), [P 0 + ρg (82.3 m)](2.50 m x)a = P 0 V bell T f T i Using P 0 = 1 atm = Pa and ρ = kg m 3 x = (2.50 m) 1 T f T 0 ρg(82.3 m) 1 + P 0 x = 2.24 m 1 = (2.50 m) K K 1 + ( kg/m 3 )(9.80 m/s 2 )(82.3 m) N/m 2 1

13 Chapter 19 Solutions 13 If the water in the bell is to be expelled, the air pressure in the bell must be raised to the water pressure at the bottom of the bell. That is, P bell = P 0 + ρg(82.3 m) = Pa kg m m s2 (82.3 m) P bell = Pa = 9.16 atm The excess expansion of the brass is L rod L tape = (α brass α steel )L i T ( L) = ( )10 6 (C ) m(35.0 C ) ( L) = m (a) The rod contracts more than tape to a length reading m m = m m m = m *19.44 At 0 C, 10.0 gallons of gasoline has mass, from ρ = m/v m = ρv = 730 kg m 3 (10.0 gal) m gal = 27.7 kg The gasoline will expand in volume by V = βv i T = ( /C )(10.0 gal)(20.0 C 0.0 C) = gal At 20.0 C, we have gal = 27.7 kg 10.0 gal = 10.0 gal (27.7 kg) = 27.2 kg gal The extra mass contained in 10.0 gallons at 0.0 C is 27.7 kg 27.2 kg = kg R B + α B R B (T 20.0) = R s + α s R s (T 20.0) cm + ( /C )(3.994 cm)(t 20.0 C) = cm + ( )(C ) 1 (4.000 cm)(t 20.0 C)

14 14 Chapter 19 Solutions T = T = 208 C

15 Chapter 19 Solutions 15 *19.46 The frequency played by the cold-walled flute is f i = v λ i = v 2L i. When the instrument warms up f f = v = v v = λ f 2L f 2L i (1 + α T) = 1 + α T The final frequency is lower. The change in frequency is f = f i f f = f i α T f = v α T 2L i 1 + α T v (α T) 2L i f i f (343 m/s)( /C )(15.0 C ) 2(0.655 m) = Hz This change in frequency is imperceptibly small Neglecting the expansion of the glass, A h h = V A β T h = 4 3 π cm 2 3 π ( cm) 2 ( /C )(30.0 C) = 3.55 cm T i T i + T (a) The volume of the liquid increases as V l = V i β T. The volume of the flask increases as V g = 3αV i T. Therefore, the overflow in the capillary is V c = V i T(β 3α); and in the capillary V c = A h. Therefore, h = V i (β 3α) T A For a mercury thermometer β(hg) = / C and for glass, 3α = / C. Thus β 3α β, or α «β (a) ρ = m V and dρ = m V 2 dv For very small changes in V and ρ, this can be expressed as ρ = m V V V = ρβ T

16 16 Chapter 19 Solutions The negative sign means that any increase in temperature causes the density to decrease and vice versa.

17 Chapter 19 Solutions 17 For water we have β = ρ ρ T = ( g/cm g/cm 3 ) ( g/cm 3 )( )C = / C (a) P 0 V T = P'V' T' V' = V + Ah k P' = P 0 + kh A P 0 + kh A (V + Ah) = P 0V T' T h 250 C 20 C N m N 105 m 3 h ( m 3 + ( m 2 )h) = N m 2 ( m 3 ) 523 K 293 K 2000h h 397 = 0 h = 2013 ± = m P' = P + kh A = Pa + ( N/m)(0.169) m 2 P' = Pa (a) We assume that air at atmospheric pressure is above the piston. In equilibrium P gas = mg A + P 0. Therefore, nrt ha = mg A + P 0 or h = nrt (mg + P 0 A) where m we have used V = ha as the volume of the gas. From the data given, Gas h h = (0.200 mol)(8.315 J/K mol)(400 K) (20.0 kg)(9.80 m/s 2 ) + ( N/m 2 )( m 2 ) = m

18 18 Chapter 19 Solutions (a) L 1 = r 1 θ = L i (1 + α 1 T) L 2 = r 2 θ = L i (1 + α 2 T) r = r 2 r 1 = L i(α 2 α 1 ) T θ r 2 r 1 r 2 r 1 = 1 θ [L i + L i α 2 T L i L i α 1 T] θ θ = L i (α 2 α 1 ) T (r 2 r 1 ) θ 0 as T 0 θ 0 as α 1 α 2 θ < 0 when T < 0 cooling means temperature is decreasing. (c) It bends the other way From the diagram we see that the change in area is A = l w + w l + w l. Since l and w are each small quantities, the product w l will be very small. Therefore, we assume w l 0. Since w = wα T and l = lα T, we then have A = lwα T + wlα T and since A = lw, we have A = 2αA T. The approximation assumes w l 0, or α T 0. Another way of stating this is α T «1. l w T i w + w T + T T i l + l (a) R = R 0 (1 + AT C 50.0 Ω = R 0 (1 + 0) R 0 = 50.0 Ω 71.5 Ω = (50.0 Ω) [1 + ( C)A] A = (C ) 1 R 0 = 50.0Ω T = 1 R A 1 1 = 89.0 R (C ) = 422 C

19 Chapter 19 Solutions (a) T i = 2π L i g L i = T2 ig 4π 2 = (1.000 s)2 (9.80 m/s 2 ) 4π 2 = m L = αl i T = ( /C )( m)(10.0 C) = m T f = 2π L i + L g = 2π m 9.80 m/s 2 = s T = s In one week, the time lost is time lost = (1 week)( s lost per second) = d 7.00 week s s lost d s = 57.4 s lost I = r 2 dm and since r(t) = r(t i )(1 + α T), for α T << 1 we find I(T) I(T i ) = (1 + α T)2, thus I(T) I(T i) I(T i ) 2α T (a) With α = / C and T = 100 C, we find for Cu: I I = 2( / C)(100 C) = 0.340% With α = / C and T = 100 C, we find for Al: I I = 2( / C)(100 C) = 0.480% (a) B = ρgv' P' = P 0 + ρgd P'V' = P 0 V i B = ρgp 0V i P' = ρgp 0 V i (P 0 + ρgd) Since d is in the denominator, B must decrease as the depth increases. (The volume of the balloon becomes smaller with increasing pressure.)

20 20 Chapter 19 Solutions (c) 1 2 = B(d) B(0) = ρgp 0V i /(P 0 + ρgd) P 0 = ρgp 0 V i /P 0 P 0 + ρgd P 0 + ρgd = 2P 0 d = P 0 ρg = N/m 2 ( kg/m 3 )(9.80 m/s 2 ) = 10.3 m (a) Let m represent the sample mass. Then the number of moles is n = m/m and the density is ρ = m/v. So PV = nrt becomes PV = m M RT or PM = m V RT Then, ρ = m V = PM RT ρ = PM RT = ( N/m 2 )( kg/mol) = 1.33 kg/m (8.315 J/mol K)(293 K) For each gas alone, P 1 = N 1kT V and P 2 = N 2kT V and P 3 = N 3kR V, etc. For all gases P 1 V 1 + P 2 V 2 + P 3 V 3... = (N 1 + N 2 + N 3...)kT and (N 1 + N 2 + N 3...)kT = PV Also, V 1 = V 2 = V 3 =... = V, therefore P = P 1 + P 2 + P (a) Using the Periodic Table, we find the molecular masses of the air components to be M(N 2 ) = u, M(O 2 ) = u, M(Ar) = u and M(CO 2 ) = u Thus, the number of moles of each gas in the sample is n(n 2 ) = n(o 2 ) = g g/mol g g/mol = mol = mol 1.28 g n(ar) = g/mol = mol n(co 2 ) = 0.05 g g/mol = mol

21 Chapter 19 Solutions 21 The total number of moles is n 0 = n i = mol. Then, the partial pressure of N 2 is P(N 2 ) = Similarly, mol mol ( Pa) = 79.1 kpa P(O 2 ) = 21.2 kpa P(Ar) = 940 Pa P(CO 2 ) = 33.3 Pa Solving the ideal gas law equation for V and using T = = K, we find V = n 0RT P = (3.453 mol)(8.315 J/mol K)( K) Pa = m 3 Then, ρ = m V = kg m3 = 1.22 kg/m3 (c) The 100 g sample must have an appropriate molar mass to yield n 0 moles of gas: that is M(air) = 100 g = 29.0 g/mol mol In any one section of concrete, length L i expands by L = αl i T = ( /C )L i (25.0 C ) = L i The unstressed length of that rail increases by ( /C )L i (25.0 C ) = L i (a) So the rail is stretched elastically by the extra L i L i = L i in F A = Y L = ( L 10 N/m)( ) = N/m 2 i Fraction of yield strength = N/m N/m2 =

22 22 Chapter 19 Solutions (a) From PV = nrt, the volume is: V = nr P T Therefore, when pressure is held constant, dv dt = nr P = V T Thus, β 1 V dv dt = 1 V V T, or β = 1 T 1 At T = 0 C = 273 K, this predicts β = 273 K = /K Experimental values are: β He = /K and β air = /K After expansion, the length of one of the spans is L f = Li(1 + α T) = (125 m)[1 + ( /C )(20.0 C )] = m L f, y, and the original 125 m length of this span form a right triangle with y as the altitude. Using the Pythagorean theorem gives: ( m) 2 = y 2 + (125 m) 2 yielding y = 2.74 m After expansion, the length of one of the spans is L f = L(1 + α T). L f, y, and the original length L of this span form a right triangle with y as the altitude. Using the Pythagorean theorem gives L 2 f = L 2 + y 2, or y = L 2 f L 2 = L (1 + α T) 2 1 = L 2α T + (α T) 2 Since α T << 1, y L 2α T For L = L s L c to be constant, the rods must expand by equal amounts: α c L c T = α s L s T L s = α c L c α s L = α c L c α s L c Lα s L c = (α c α s ) = 5.00 cm( /C ) ( /C = 9.17 cm /C ) Lα c and L s = (α c α s ) = 5.00 cm = 14.2 cm

23 Chapter 19 Solutions 23

24 24 Chapter 19 Solutions (a) With piston alone: T = constant, so PV = P 0 V i or P(Ah 0 ) = P 0 (Ah i ) 50.0 cm With A = constant, P = P 0 h i h 0 (a) But, P = P 0 + m pg A the piston., where m p is the mass of h i h to Thus, P 0 + m pg A = P 0 h i h 0, which reduces (c) h 0 = h i 1 + m pg P 0 A = cm (20.0 kg)(9.80 m/s 2 = cm ) ( Pa)π(0.400 m) 2 With the man of mass M on the piston, a very similar calculation (replacing m p by m p + M) gives: h' = h i 1 + (m p + M)g P 0 A = cm (95.0 kg)(9.80 m/s 2 = cm ) ( Pa)π(0.400 m) 2 Thus, when the man steps on the piston, it moves downward by h = h 0 h' = cm cm = cm = 7.10 mm P = const, so V T = V' or Ah 0 T i T = Ah' T i, giving T = T h 0 i h ' = (293 K) = 297 K (or 24 C)

25 Chapter 19 Solutions (a) dl L = αdt T iαdt = T i L i dl Li L ln L f L i = α T L f = L i e α T L f = (1.00 m)e [ (C ) 1 ](100 C) = m L' f = (1.00 m) [1 + ( / C)(100 C)] = m L f L' f L f = = % L f = (1.00 m)e [ ( C) 1 ](100 C) = m L' f = (1.00 m)[1 + (0.0200/ C)(100 C)] = m L f L' f L f = 59.4% At 20.0 C, the unstretched lengths of the steel and copper wires are L s (20.0 C) = (2.000 m)[ )(C ) 1 ( 20.0 C)] = m L c (20.0 C) = (2.000 m)[ )(C ) 1 ( 20.0 C)] = m Under a tension F, the length of the steel and copper wires are L' s = L s 1 + F YA s L' c = L c 1 + F YA c where L' s + L' c = m Since the tension, F, must be the same in each wire, solve for F: F = (L' s + L' c ) (L s + L c ) L s L c + Y s A s Y c A c When the wires are stretched, their areas become A s = π( m) 2 [1 + ( )( 20.0)] 2 = m 2 A c = π( m) 2 [1 + ( )( 20.0)] 2 = m 2 Recall Y s = Pa and Y c = Pa. Substituting into the equation for F, we obtain m ( m m) F = m ( Pa)( ) m m ( Pa)( ) m 2 F = 125 N

26 26 Chapter 19 Solutions To find the x-coordinate of the junction, L' s = ( m) 125 N 1 + ( N/m 2 )( m 2 ) = m Thus the x-coordinate is = m (a) µ = πr 2 ρ = π( m) 2 ( kg/m 3 ) = kg/m f 1 = v 2L and v = T µ so f 1 = 1 2L T µ Therefore, T = µ(2lf 1 ) 2 = ( )( ) 2 = 632 N (c) First find the unstressed length of the string at 0 C: L = L natural 1 + T AY L so L natural = 1 + T/AY A = π( m) 2 = m 2 and Y = Pa Therefore, T AY = 632 ( )( ) = , and L natural = (0.800 m) ( ) = m The unstressed length at 30.0 C is L 30 C = L natural [1 + α(30.0 C 0.0 C)], or L 30 C = ( m)[1 + ( )(30.0)] = m Since L = L 30 C 1 + T' AY, where T' is the tension in the string at 30.0 C, T' = AY L 1 = ( L 30 C 7 )( ) = 580 N To find the frequency at 30.0 C, realize that f ' 1 f 1 = T' T so f ' 1 = (200 Hz) 580 N = 192 Hz 632 N

27 Chapter 19 Solutions Let 2θ represent the angle the curved rail subtends. We have L i + L = 2θR = L i (1 + α T) and sin θ = L i/2 R = L i 2R h L i /2 L i /2 Thus, θ = L i (1 + α T) = (1 + α T) sin θ 2R R R and we must solve the transcendental equation θ θ = (1 + α T) sin θ = ( ) sin θ Homing in on the non-zero solution gives, to four digits, θ = rad = Now, h = R R cos θ = L i(1 cos θ) 2 sin θ This yields h = 4.54 m, a remarkably large value compared to L = 5.50 cm.

Chapter 10. Answers to Even Numbered Problems. 2. (a) 251 C. (b) 1.36 atm C, C. 6. (a) 273 C (b) 1.27 atm, 1.74 atm

Chapter 10. Answers to Even Numbered Problems. 2. (a) 251 C. (b) 1.36 atm C, C. 6. (a) 273 C (b) 1.27 atm, 1.74 atm hapter Answers to Even Numbered Problems. (a) 5 (b).6 atm 4. 56.7, -6. 6. (a) 7 (b).7 atm,.74 atm 8. (a) 8 F (b) 45 K. (a) 6 (b) 6. (a) L. m.49 mm (b) fast 4..9 8. 8.7 m..5 km, accordion-like expansion