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Unformatted text preview: 2 For correctly accounting for atmospheric pressure (with no obvious algebraic errors) leading to an answer P0 is atmospheric pressure, and Pp = P0 + Pgauge + Pgauge = Pp  P0 = 3.16 10 4 Pa (or 3.23 10 4 Pa using g = 10 m s2 ) ( )( ) ) 1 point 1 point 2008 The College Board. All rights reserved. Visit the College Board on the Web: www.collegeboard.com. AP PHYSICS B 2008 SCORING GUIDELINES
Question 5
10 points total Distribution of points (a) 3 points Process A B B C C A W 0  + Q + +  DU + 0 
1 point 1 point 1 point For correctly identifying the signs of all three variables (W , DU , Q ) for process A B For correctly identifying the signs of all three variables (W , DU , Q ) for process B C For correctly identifying the signs of all three variables (W , DU , Q ) for process C A (b) 4 points For a correct explanation of why zero work is done on the gas Examples of correct responses include: There is no area under the graph/curve. There is no volume change. The piston does not move. W =  P DV , where DV = 0 . W = 0 by definition in an isochoric/isovolumetric process. For a correct explanation of why DU is positive Examples of correct responses include: For a fixed number of moles of a sample, an increase in pressure at constant volume implies an increase in temperature, and an increased temperature implies an increase in internal energy ( DU is positive). State B is on a higher isotherm than state A. 3 U = nRT ; since T increases, DU is positive. 2 U = 3 PV ; since P increases at a constant V, DU is positive. 2 1 point 1 point A correct use of the first law of thermodynamics leading to DU being positive ( DU = Q + W , but W = 0 so DU = Q ; since Q is positive, DU must be also). For a correct explanation of why Q is positive Examples of correct responses include: If pressure increases and volume is constant, heat must be added to system. If temperature increases and volume is constant, heat must be added to system. A correct use of the first law of thermodynamics leading to Q being positive ( DU = Q + W , but W = 0 so DU = Q ;...
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 Spring '11
 DavidNewton
 Physics

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