_ap05_sg_physics_b_fo_46690

_ap05_sg_physics_b_fo_46690 - AP® Physics B 2005 Scoring...

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Unformatted text preview: AP® Physics B 2005 Scoring Guidelines Form B The College Board: Connecting Students to College Success The College Board is a not-for-profit membership association whose mission is to connect students to college success and opportunity. Founded in 1900, the association is composed of more than 4,700 schools, colleges, universities, and other educational organizations. Each year, the College Board serves over three and a half million students and their parents, 23,000 high schools, and 3,500 colleges through major programs and services in college admissions, guidance, assessment, financial aid, enrollment, and teaching and learning. Among its best-known programs are the SAT®, the PSAT/NMSQT®, and the Advanced Placement Program® (AP®). The College Board is committed to the principles of excellence and equity, and that commitment is embodied in all of its programs, services, activities, and concerns. Copyright © 2005 by College Board. All rights reserved. College Board, AP Central, APCD, Advanced Placement Program, AP, AP Vertical Teams, Pre-AP, SAT, and the acorn logo are registered trademarks of the College Entrance Examination Board. Admitted Class Evaluation Service, CollegeEd, Connect to college success, MyRoad, SAT Professional Development, SAT Readiness Program, and Setting the Cornerstones are trademarks owned by the College Entrance Examination Board. PSAT/NMSQT is a registered trademark of the College Entrance Examination Board and National Merit Scholarship Corporation. Other products and services may be trademarks of their respective owners. Permission to use copyrighted College Board materials may be requested online at: http://www.collegeboard.com/inquiry/cbpermit.html. Visit the College Board on the Web: www.collegeboard.com. AP Central is the official online home for the AP Program and Pre-AP: apcentral.collegeboard.com. AP PHYSICS B 2005 SCORING GUIDELINES (Form B) General Notes About 2005 AP Physics Scoring Guidelines 1. The solutions contain the most common method(s) of solving the free-response questions and the allocation of points for these solutions. Other methods of solution also receive appropriate credit for correct work. 2. Generally, double penalty for errors is avoided. For example, if an incorrect answer to part (a) is correctly substituted into an otherwise correct solution to part (b), full credit will usually be awarded. One exception to this may be cases when the numerical answer to a later part should be easily recognized as wrong, e.g., a speed faster than the speed of light in vacuum. 3. Implicit statements of concepts normally receive credit. For example, if use of the equation expressing a particular concept is worth one point, and a student’s solution contains the application of that equation to the problem but the student does not write the basic equation, the point is still awarded. 4. The scoring guidelines typically show numerical results using the value g 9.8 m s 2 , but use of 10 m s 2 is of course also acceptable. 5. Numerical answers that differ from the published answer due to differences in rounding throughout the question typically receive full credit. The exception is usually when rounding makes a difference in obtaining a reasonable answer. For example, suppose a solution requires subtracting two numbers that should have five significant figures and that differ starting with the fourth digit (e.g., 20.295 and 20.278). Rounding to three digits will lose the accuracy required to determine the difference in the numbers, and some credit may be lost. Copyright © 2005 by College Entrance Examination Board. All rights reserved. Visit apcentral.collegeboard.com (for AP professionals) and www.collegeboard.com/apstudents (for AP students and parents). 2 AP PHYSICS B 2005 SCORING GUIDELINES (Form B) Question 1 10 points total (a) Distribution of points 2 points For an upward force with a label indicating a normal force or a force from the scale For a downward force with a label appropriate for a weight One point was deducted for each extraneous force until the net score was zero. (b) 1 point 1 point 3 points The scale reading is the magnitude of the normal force on the student. For starting with Newton’s second law Fnet ma For correctly expressing the net force N mg ma For correctly solving for the normal force N mg a 1 point 1 point 1 point (c) (i) 2 points The normal force exerted by the scale is maximum when the acceleration has its maximum positive value. The force is maximum from 12 to 16 seconds. For an interval beginning at 12 seconds For an interval ending at 16 seconds One point was deducted for each interval with no correct endpoints until the net score was zero. (ii) 1 point 1 point 1 point Using the expression for the normal force from part (b) N mg a N 45 kg 9.8 m s2 N 1.2 m s2 45 kg 11.0 m s2 For the correct answer with units N 500 N 1 point Copyright © 2005 by College Entrance Examination Board. All rights reserved. Visit apcentral.collegeboard.com (for AP professionals) and www.collegeboard.com/apstudents (for AP students and parents). 3 AP PHYSICS B 2005 SCORING GUIDELINES (Form B) Question 1 (continued) Distribution of points (d) 2 points The speed of the elevator is constant when the acceleration is zero. This occurs from 7 to 10 seconds and from 17 to 20 seconds. For each correct interval One point was deducted for each extraneous interval until the net score was zero. One point was awarded if the scale was misread for both intervals and the response was given as both 6.5 to 10 and 16.5 to 20. 1 point each Copyright © 2005 by College Entrance Examination Board. All rights reserved. Visit apcentral.collegeboard.com (for AP professionals) and www.collegeboard.com/apstudents (for AP students and parents). 4 AP PHYSICS B 2005 SCORING GUIDELINES (Form B) Question 2 10 points total Distribution of points (a) (i) 2 points For each correctly drawn and labeled force One point was deducted if any extraneous forces were shown. (ii) 2 points For each correctly drawn and labeled force One point was deducted if any extraneous forces were shown. (b) 1 point each 1 point each 2 points For correctly applying conservation of energy 12 mu mg Dh 2 u 2 g Dh u 2 9.8 m s2 0.08 m 1 point 1.568 m s For the correct answer u 1.3 m s 1 point Copyright © 2005 by College Entrance Examination Board. All rights reserved. Visit apcentral.collegeboard.com (for AP professionals) and www.collegeboard.com/apstudents (for AP students and parents). 5 AP PHYSICS B 2005 SCORING GUIDELINES (Form B) Question 2 (continued) Distribution of points (c) 3 points 1 point For using F ma For a correct expression for the net force that is equated to a centripetal force T mg T mg T 1 point 2 mu r u2 r 0.085 kg 9.8 m s2 1.3 m s 2 1.5 m For the correct answer with units T (d) 1 point 0.93 N (or equivalent answer depending on rounding or use of g 2 10 m s ) 1 point For a correct modification For example: Make the string four times longer. 1 point Copyright © 2005 by College Entrance Examination Board. All rights reserved. Visit apcentral.collegeboard.com (for AP professionals) and www.collegeboard.com/apstudents (for AP students and parents). 6 AP PHYSICS B 2005 SCORING GUIDELINES (Form B) Question 3 15 points total (a) Distribution of points 4 points For any mathematical statement indicating that the force on the Q charge is obtained by the addition of forces due to the other two charges For any of the following three statements or expressions The y components of the forces due to the two 2Q charges cancel. The magnitude of the net force equals the sum of the magnitudes of the x components. r Fx r a a2 a 2a 2 5a kQ 2Q cos q r2 2a 2a 2 cos q r 5a 5 kQ 2Q 2 Fx 2 5 5a 2 For the correct expression for the magnitude of the net force 8kQ 2 Fx 5 5a 2 For the correct indication of direction Force is directed to the right, OR force is in the +x direction, OR explicit use of an arrow to show direction. (b) 2 1 point 1 point 1 point 1 point 3 points For any indication that the contributions to the field from the 2Q charges cancel For the correct expression for the magnitude of the field due to the Q charge E E kq r 2 k 1 point 1 point Q 2a 2 kQ (point awarded even with a minus sign) 4a 2 For the correct indication of direction Field is directed to the right, OR field is in the +x direction, OR explicit use of an arrow to show direction. 1 point Copyright © 2005 by College Entrance Examination Board. All rights reserved. Visit apcentral.collegeboard.com (for AP professionals) and www.collegeboard.com/apstudents (for AP students and parents). 7 AP PHYSICS B 2005 SCORING GUIDELINES (Form B) Question 3 (continued) Distribution of points (c) 5 points V k i qi ri For any indication of the need to use superposition for the electrical potential (or showing three terms in the expression) One point awarded for each correct term, including the minus sign, in the following expression k 2Q k 2Q kQ V a a 2a 4 kQ kQ 8kQ kQ V a 2a 2a 2a For the correct simplified answer with correct sign 9kQ V 2a (d) 1 point 3 points 1 point 3 points For having F = 0 at x = 0 with F increasing gradually going away from the origin This point was not given for a spike function at the origin. For having the graph positive on the right and negative on the left For having a single maximum of F on each side of the origin and having the curve monotonically and asymptotically decreasing to zero as x 1 point 1 point 1 point Copyright © 2005 by College Entrance Examination Board. All rights reserved. Visit apcentral.collegeboard.com (for AP professionals) and www.collegeboard.com/apstudents (for AP students and parents). 8 AP PHYSICS B 2005 SCORING GUIDELINES (Form B) Question 4 15 points total Distribution of points Credit for each part of this problem was awarded if the response, when judged holistically, showed reasonable understanding of a correct experimental method. Responses that showed little understanding could not receive full credit. (a) 2 points For using in parts (b) and (c) every piece of equipment marked in part (a) For marking every piece of equipment used in parts (b) and (c) (b) 1 point 1 point 4 points For drawing an appropriate setup For completely labeling the equipment For indicating the measurements to be made For complete labeling of the measurements, including symbols for them 1 point 1 point 1 point 1 point Sample response (c) 4 points For a description of the setup of equipment For a description of how to determine maxima or minima in the interference pattern For indicating what measurements to take Example response for the figure above: Set the speakers a fixed distance d apart, pointing perpendicular to the line along which d is measured. Determine a line parallel to the speaker line and a distance L away. Use the sound meter to locate the maxima of the interference pattern along this line. Record the locations of these maxima along the line. 2 points 1 point 1 point Copyright © 2005 by College Entrance Examination Board. All rights reserved. Visit apcentral.collegeboard.com (for AP professionals) and www.collegeboard.com/apstudents (for AP students and parents). 9 AP PHYSICS B 2005 SCORING GUIDELINES (Form B) Question 4 (continued) Distribution of points (d) 4 points The solution shown below is for the example given above. Solutions for other methods also received appropriate credit. For the condition for a maximum ml d sin q For using the condition for small angles and eliminating q sin q y L ml dy L For using successive maxima (i.e., Dm 1 ) to get l d Dy L For an appropriate expression for frequency f usound l f (e) 1 point 1 point 1 point 1 point Lusound d Dy 1 point For a correct description For the example given: Decreasing frequency results in increasing wavelength. Thus the distance between successive maxima will increase. 1 point Copyright © 2005 by College Entrance Examination Board. All rights reserved. Visit apcentral.collegeboard.com (for AP professionals) and www.collegeboard.com/apstudents (for AP students and parents). 10 AP PHYSICS B 2005 SCORING GUIDELINES (Form B) Question 5 10 points total (a) Distribution of points 4 points For including atmospheric pressure in the expression for total pressure For the correct expression for the term for the pressure due to the saltwater P Patm rsw gh P 1 105 Pa 1025 kg m 3 9.8 m s2 20 m P 1 105 Pa 2.0 105 Pa P 3.0 105 Pa (or 3.1 105 Pa using g 10 m s2 ) For the correct relationship between force and pressure F PA F 3.0 105 Pa 4.0 10 5 m 2 For the correct answer with units F 12 N (b) 1 point 1 point 1 point 1 point 4 points For applying Bernoulli’s principle at the top of the tank and the height of the drain 12 12 P0top r gytop ru P0 drain r gydrain ru 2 top 2 drain For realizing that P0top P0 drain Patm 1 point For realizing that utop 1 point 0 Substituting and simplifying 12 r gytop r gydrain ru 2 drain 12 ru r gydrain r gytop 2 drain udrain 2 g ydrain udrain r g ydrain 1 point ytop ytop 2 9.8 m s2 20 m udrain 392 m s For the correct answer with units udrain 20 m s 1 point Copyright © 2005 by College Entrance Examination Board. All rights reserved. Visit apcentral.collegeboard.com (for AP professionals) and www.collegeboard.com/apstudents (for AP students and parents). 11 AP PHYSICS B 2005 SCORING GUIDELINES (Form B) Question 5 (continued) Distribution of points (c) 2 points For a correct expression for the volume rate of flow V t uA Vt 20 m s 4.0 10 5 m2 For the correct answer with units Vt 8.0 10 4 1 point 1 point 3 ms Copyright © 2005 by College Entrance Examination Board. All rights reserved. Visit apcentral.collegeboard.com (for AP professionals) and www.collegeboard.com/apstudents (for AP students and parents). 12 AP PHYSICS B 2005 SCORING GUIDELINES (Form B) Question 6 10 points total (a) Distribution of points 1 point For a correct expression relating P and V 1 PV nRT OR P nRT V (b) 1 point 2 points The total pressure is atmospheric pressure plus the pressure due to the added mass. mg P Patm A m 9.8 m s2 P 1.0 105 P a 3.0 10 4 m 2 m ( g) k V m3 1V m 3 P a) P ( 0 6.0 10 5 1.7 10 4 1.0 105 1 4.5 10 5 2.2 10 4 1.3 10 5 2 3.6 10 5 2.8 10 4 1.7 105 3 3.0 10 5 3.3 10 4 2.0 10 5 4 2.6 10 5 3.8 10 4 2.3 105 For two or three correct values of pressure For an additional one or two correct values (i.e., four or five correct received two points) If atmospheric pressure was left out, only one point could be earned. 1 point 1 point Copyright © 2005 by College Entrance Examination Board. All rights reserved. Visit apcentral.collegeboard.com (for AP professionals) and www.collegeboard.com/apstudents (for AP students and parents). 13 AP PHYSICS B 2005 SCORING GUIDELINES (Form B) Question 6 (continued) Distribution of points (c) 3 points For correctly labeling the horizontal axis For correctly labeling the vertical axis For accurately plotting the points Full credit could be earned for correctly plotting incorrect data from the table. 1 point 1 point 1 point Example answer shown below. This part of the question did not ask for the best-fit line, but it was needed for part (d) and was graded in that part. (d) 4 points For drawing a reasonable best-fit line through the data, given that the data could yield a value for n P nRT 1 V For calculating the slope of the line From the example graph shown above, where the line goes through the first and last data points 2.3 105 1.0 105 Pa slope 3.8 10 4 1.7 10 4 m 3 For a reasonable value for the slope For the values shown above, slope n slope RT 1 point 1 point 1 point 6.19 a m P 3 6.19 P m3 a 8.31 J mol K 300 K For the correct answer n 0.0025 mol n 1 point Copyright © 2005 by College Entrance Examination Board. All rights reserved. Visit apcentral.collegeboard.com (for AP professionals) and www.collegeboard.com/apstudents (for AP students and parents). 14 AP PHYSICS B 2005 SCORING GUIDELINES (Form B) Question 7 10 points total (a) Distribution of points 2 points For a correct expression for the energy of a photon E hf OR E hc l Substituting into the second equation E 1.99 10 25 Jm 450 10 9 m OR 1 point 1.24 103 eV nm 450 nm For the correct answer with units E 4.4 10 19 J (or 2.8 eV) (b) 1 point 3 points For a correct relationship for the number of photons N energy emitted in 5 minutes N energy per photon For correct substitutions 2.5 10 3 J s 5 min 60 s min power time N energy per photon 4.4 10 19 J For the correct answer N 1.7 1018 (c) 1 point 1 point 1 point 3 points For relating the maximum kinetic energy of an electron to the stopping potential (i.e., 0.86 eV or qV) 12 mu qV 2 max For obtaining the correct expression for the maximum speed umax 2qV m umax 2 1.6 10 19 C 0.86 V 9.11 10 31 For the correct answer with units umax 5.5 105 m s 1 point 1 point kg 1 point Copyright © 2005 by College Entrance Examination Board. All rights reserved. Visit apcentral.collegeboard.com (for AP professionals) and www.collegeboard.com/apstudents (for AP students and parents). 15 AP PHYSICS B 2005 SCORING GUIDELINES (Form B) Question 7 (continued) Distribution of points (d) 2 points For a correct relationship for the wavelength h l pmax l l 1 point h mumax 6.63 1034 J s 9.11 10 31 kg 5.5 105 m s For the correct answer with units l 1.3 nm 1 point Copyright © 2005 by College Entrance Examination Board. All rights reserved. Visit apcentral.collegeboard.com (for AP professionals) and www.collegeboard.com/apstudents (for AP students and parents). 16 ...
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