PHYS 122 Midterm 2 solutions

PHYS 122 Midterm 2 solutions - Why 122 — 630th Whammy...

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Unformatted text preview: Why; 122 — 630th Whammy @@ warm 2 7 November ‘2007 TRUE OR FALSE W116 a gas is taken through an adiabatic‘expansion, I: the pressure Of the 86.5 decreases. T the volume of the gas decreases. T work is done on the gas. T the internal energy of the gas increases. MULTIPLE CHOICE I. My grandfather made two clocks: one for me, and one for my sister. The sphere on the end ot the pendulum in my clock is twice as massive. How should he adjust the length of the pendulum in my clock to oscillate with the same period as my sister’s clock? a) He should make it twice as long. 1)) He should make it halt as long. Q) He doesn’t need to do any thing to the length. cl) There isn‘t enough information to tell what he should do. 2. When two water waves interfere with each other, which of the following occurs? @ The two waves pass through each other with no loss of energy. la) The two waves lose energy when interfering. c) During superposition, the resulting amplitude is the difference of the individual amplitudes d) The superposition depends on whether the interfering waves are transverse or longitudinal. SHORT ANSWER With the installation of air conditioning units in subway cars, tunnels and plattorms in subway stations can become unbearably hot in the summer. With what you know of thermodynamics, explain why this is so inefficient. Think of one way to alleviate this problem. TIM, (Lia Goad/thaw twp; mid air (.Cpc.) ow-t- 0+ “HP-L cm Mal emu—s [4.0+ 0.414. (CPA wL-t‘b uHA-l. MM‘S W “WW-C 1+ to “#:cm't‘ MC'MQL. each M m. +6.4, Mg. (09.; was.) +0 thevwth. +04 ‘Pvabbovu a +1: ws—l-a—U low»; 41: .9.le Marta/1A— It'b, OY al/YW Warm w {vow +04 shout; above. M Ouellette, 6 November 2007 Page 1 0t 4 PROBLEMS I. The Stirling engine which sat on Ry an's hand during our in~class demonstration operates through an isothermal expansion (L?) at 57°C, an isometric process (9—3)), an isothermal compression (5-4) at 99°C, and another isometric process (4-1), in that order. 0.) Draw this cycle on a p V—vdiagram, indicating the direction in which the cycle operates. Be sure to properly label your axes and label which isotherm is which. , ‘7 l‘ . , 34°C 7— " 21% 3 v‘ V; V b) If one mole of a monatomic gas is taken through this cycle where V2 = 1. 5 V1. What is the work done in each recess? Show yOur work but place your final answers in the table. T‘_l=5=\«+z=r3=5\o\¢ X7516 1/;st V V LS T3.“ = Z2.+’L=t3 = 295K =lmol WP; = MZTQM (113-) = COC83tX3lo) 9M (15) Wrz ‘ 4045.5 W34 = n [2'1”er (1%) a. m :21— w(¥,‘;)=(\)(g.31x296)as(o.m) Ws—A ‘ “ 99 2 J c) What is the net work done in the Stirling engine cycle? WM = W": 4* W11 + W3-4 ‘V’ W4-t .=4045J + o + DJ: 0982) Want 1“ b3) (1) Evaluation. Compare your answers to part (a) and (c). Are they consistent with each other? Explain briefly. Yes - vwou. PDSl-t’tvt wed:— in AM on ex PMSL‘W 4km Maud-tn: W W mwssiw, MA as.» Page“ nam'w. «page? Cc) We M. 5 +1~L s MOuellette,6Novembe19007 Paae20t4 PROBLEMS (cont) ‘2. A 754(5) circus performer jumps from a height at 5.0 m onto a trampoline which then stretches down 0.50 m. a) If we model the performer and trampoline as a mass-aspiring system, what is its spring constant? W\'.= 1'5 k3 U: E5 In“: 5.0M I 1 Mat” 1kA A = 0-3w‘ 9 k = 1mg“ ' 2L4€lcaX9.8Mls‘)(€-Om) k = . A1 ’ (0.3m): \4= 3'.an ”m b) Plot the motion of the performer as a iunctionot time, it a clock is started when the trampoline is first stretched the most. Properly label your axes. YCM) T-r— WP;- == Z-rr( 3—1—5 “ U? to“ ”In "L T?- O.\9S 'tCs) c) Write an equation for this motion. Include numerical values where appropriate. yc+)= —AwsC«}b) 09" ’—F= y (4:) = ~t0.3m:] cos [(33'““/s)t] M. Ouellette, 6 November 9007 Page .5 of 4 PROBLEMS (cont) 5. A bat emits an ultrasound wave of frequency 50 kHz to avoid hitting a tree. a) What type of wave is this, longitudinal, or transverse? Map—Fuw-ut In a, Sou/“d way-o b) It sound travels at a speed of 543 m/s, what is the wavelength of this particular wave? w=345ml$ 0.1L; *4? x52_343m15 - £5 SO'leH'i- 'f' ’ SD'lOBHI A ‘- b.8b'l0'3w‘ c) It the maximum displacement of a particle in air is 91.108 m,wl1at is the maximum speed of an air particle as this wave passes lag? A = 2‘10'3m UM, = Au: Um»: "" C? " A (1115-) 5 210—3..“ (Zn-.9010! H1) ”W = b.28'l0‘5w‘l5 M. Ouellette, 6 November 9007 Page 4 0! 4 ...
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