_ap06_physicsb_sg_formb

_ap06_physicsb_sg_formb - AP® Physics B 2006 Scoring...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: AP® Physics B 2006 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 5,000 schools, colleges, universities, and other educational organizations. Each year, the College Board serves seven 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. © 2006 The 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 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 Board. PSAT/NMSQT is a registered trademark of the College Board and National Merit Scholarship Corporation. All other products and services may be trademarks of their respective owners. Permission to use copyrighted College Board materials may be requested online at: 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: apcentral.collegeboard.com. AP® PHYSICS B 2006 SCORING GUIDELINES (Form B) General Notes About 2006 AP Physics Scoring Guidelines 1. The solutions contain the most common method of solving the free-response questions and the allocation of points for this solution. Some also contain a common alternate solution. 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 1 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. However, when students are asked to derive an expression, it is normally expected that they will begin by writing one or more fundamental equations, such as those given on the AP Physics exam equation sheet. See pages 21–22 of the AP Physics Course Description for a description of the use of such terms as “derive” and “calculate” on the exams, and what is expected for each. 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. Solutions usually show numerical answers using both values when they are significantly different. 5. Strict rules regarding significant digits are usually not applied to numerical answers. However, in some cases answers containing too many digits may be penalized. In general, two to four significant digits are acceptable. Numerical answers that differ from the published answer due to differences in rounding throughout the question typically receive full credit. Exceptions to these guidelines usually occur 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. © 2006 The College 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 2006 SCORING GUIDELINES (Form B) Question 1 15 points total (a) Distribution of points 3 points For a line that is close to all of the data points For a smooth curve For a nonlinear curve that is concave up (b) 1 point 1 point 1 point 2 points 12 gt 2 For a correct pair of quantities, expressed in terms of D and t, that will yield a straight line Distance and time are related by the equation D = Examples: D and t 2 OR 2 points D and t © 2006 The College Board. All rights reserved. Visit apcentral.collegeboard.com (for AP professionals) and www.collegeboard.com/apstudents (for students and parents). 3 AP® PHYSICS B 2006 SCORING GUIDELINES (Form B) Question 1 (continued) Distribution of points (c) 4 points For correctly scaling and labeling the horizontal axis for a quantity cited in part (b) For correctly scaling and labeling the vertical axis for a quantity cited in part (b) For a reasonably correct plotting of the data For a reasonably straight line through the data points 1 point 1 point 1 point 1 point Example graphing D versus t 2 : Note: If part (b) contains incorrect variables and they are correctly graphed in part (c), a maximum of 2 points could be earned. (d) 3 points For determining the slope of the line drawn on the graph (2.0 - 0.1) m 1.9 m Using the example graph above, slope = = = 4.9 m s2 2 2 0.39 s (0.41 - 0.02 ) s For an expression relating g to the slope 1 1 In the example given, D = gt 2 , so g = slope 2 2 1 point For a value of g in the range 9-11 m s2 1 point ( 1 point ) In the example given, g = 2 4.9 m s2 = 9.8 m s2 (e) 3 points For a good, specific improvement For an explanation of how this would improve accuracy Example: Do several trials for each value of D and take averages. This reduces personal and random error. One point could be earned for less appropriate or less specific answers, for example “do trials in a vacuum” or “cut down on air resistance.” 2 points 1 point © 2006 The College Board. All rights reserved. Visit apcentral.collegeboard.com (for AP professionals) and www.collegeboard.com/apstudents (for students and parents). 4 AP® PHYSICS B 2006 SCORING GUIDELINES (Form B) Question 2 15 points total (a) Distribution of points 4 points For any use of conservation of energy For example, initially the small block has only potential energy, and it is all converted to kinetic energy when it reaches the bottom of the ramp. For a correct expression for the initial potential energy For a correct expression for the kinetic energy at the bottom of the ramp 1 2 Mgh = M (3.5u0 ) 2 For the correct answer 2 3.52 u0 or equivalent h= 2g (b) 1 point 1 point 1 point 4 points For any use of conservation of momentum For a correct expression for the initial momentum of the blocks For a correct expression for the final momentum of the blocks M (3.5u0 ) = M u + (1.5M ) (2u0 ) u = 3.5u0 - 3u0 For the correct answer u = 0.5u0 (c) 1 point 1 point 1 point 1 point 1 point 4 points For a correct relationship between friction and the acceleration of the block  F = ma = f fric 1 point For a correct kinematic equation relating acceleration and distance that does not contain time 2 u f = ui2 - 2 aD 1 point For using the correct initial speed of the block 1 point 0= 2 4u0 - 2aD a= D Substituting expressions for a and f into the first equation above 2 (1.5M ) 2 u0 D = m (1.5M ) g For the correct answer 2 m = 2u0 Dg 2 2u0 1 point © 2006 The College Board. All rights reserved. Visit apcentral.collegeboard.com (for AP professionals) and www.collegeboard.com/apstudents (for students and parents). 5 AP® PHYSICS B 2006 SCORING GUIDELINES (Form B) Question 2 (continued) Distribution of points (c) (continued) Alternate solution For any indication that the work done on the block as it slides is equal to its initial kinetic energy 1 f fric d = mui2 2 For a correct expression for the work done on the block For a correct expression for the initial kinetic energy of the block 1 2 m (1.5M ) gD = (1.5M ) (2u0 ) 2 For the correct answer 2u 2 m= 0 Dg (d) Alternate points 1 point 1 point 1 point 1 point 3 points For indicating that the collision is inelastic For indicating that the reason it is inelastic is because the change in kinetic energy is not zero, or because kinetic energy is lost in the collision For showing that the change in kinetic energy is not zero 1 1 1 2 2 2 DK = K f - K i = È M (0.5u0 ) + (1.5 M ) (2u0 ) ˘ - M (3.5u0 ) Í2 ˙2 2 Î ˚ 1 point 1 point 1 point 2 DK = -3M u0 © 2006 The College Board. All rights reserved. Visit apcentral.collegeboard.com (for AP professionals) and www.collegeboard.com/apstudents (for students and parents). 6 AP® PHYSICS B 2006 SCORING GUIDELINES (Form B) Question 3 15 points total (a) Distribution of points 2 points For indicating the correct direction for the force due to the +Q charge ( F1 as drawn above) For indicating the correct direction for the force due to the -Q charge ( F2 as drawn above) (b) 1 point 1 point 6 points For any indication that the magnitudes of F1 and F2 are the same The x-components of F1 and F2 cancel. For any indication that the magnitude of the net force is the sum of the y-components of F1 and F2 , which are equal Example: Ftotal = F1 cos q + F2 cos q = 2 F cos q , where q is the angle between the y-axis and the dashed lines in the figure For a correct expression for cos q d cos q = 2 x + d2 For a correct substitution for F into the above expression for Ftotal F= kqQ = ( 1 point 1 point 1 point kqQ x + d2 kqQ d Ftotal = 2 2 2 2 x + d x + d2 For the correct magnitude of the total force 2 kqQd Ftotal = or equivalent 32 x2 + d 2 r 2 1 point 2 1 point ) For indicating the correct direction for the total force, e.g., negative y-direction, toward the bottom of the page, etc. 1 point © 2006 The College Board. All rights reserved. Visit apcentral.collegeboard.com (for AP professionals) and www.collegeboard.com/apstudents (for students and parents). 7 AP® PHYSICS B 2006 SCORING GUIDELINES (Form B) Question 3 (continued) Distribution of points (c) 2 points The field can be found from the force. E = Ftotal q For the correct magnitude of the electric field 2 kQd E= 32 2 x + d2 1 point For indicating the correct direction for the electric field, e.g., negative y-direction, toward the bottom of the page, etc. 1 point ( (d) ) 2 points The total potential is the sum of the individual point charge potentials. kQ - kQ V = V1 + V2 = + 2 2 x +d x2 + d 2 For indicating that the electric potential is zero Note: One point partial credit could be earned for only recognizing that the potentials from the two charges must be added. (e) 2 points 3 points For any indication that as x gets large, the hypotenuse and x are approximately equal or d is negligible compared to x 1 point For indicating that the above implies that x 2 + d 2 ª x For indicating that substituting the approximate equality into the answer from part (b) 2 kqQd yields Ftotal = x3 1 point 1 point © 2006 The College Board. All rights reserved. Visit apcentral.collegeboard.com (for AP professionals) and www.collegeboard.com/apstudents (for students and parents). 8 AP® PHYSICS B 2006 SCORING GUIDELINES (Form B) Question 4 15 points total Distribution of points (a) (i) 2 points For drawing a reflected ray at approximately the same angle to the normal as the incident ray For clearly indicating that this is the reflected ray 1 point 1 point (ii) 4 points Snell’s law is used to find the angle of refraction n1 sin q1 = n2 sin q2 For correctly substituting values into Snell’s law 1.0 sin 27∞ = 1.51sin q2 sin q2 = sin 27∞ 1.51 = 0.30 For the correct value of the angle q2 = 17.5∞ For drawing a ray at approximately the correct angle For clearly indicating that this is the refracted ray 1 point 1 point 1 point 1 point (iii) 1 point The speed in the block can be determined using the definition of index of refraction. u = c n = 3.00 ¥ 108 m s 1.51 ( ) For the correct answer u = 1.99 ¥ 108 m s 1 point © 2006 The College Board. All rights reserved. Visit apcentral.collegeboard.com (for AP professionals) and www.collegeboard.com/apstudents (for students and parents). 9 AP® PHYSICS B 2006 SCORING GUIDELINES (Form B) Question 4 (continued) Distribution of points (a) (continued) (iv) 2 points For a statement that the frequency is the same in the two materials, or an equation that is an application of that fact uplastic u f = air = lair lplastic l OR l plastic = air n uplastic lair lplastic = uair 1 point } lplastic = 1.99 ¥ 108 m s (650 nm ) 3 ¥ 10 m s For the correct answer with units lplastic = 431 nm OR 430 nm (b) 8 OR l plastic = 650 nm 1.51 1 point 2 points The following points were only awarded if rays were shown or described in part (a) For indicating that the angle of reflection does not change For indicating that the angle of refraction becomes smaller 1 point 1 point (c) (i) 2 points Example in which the dark lines in the drawn pattern represent the bright bands of blue light For indicating a central peak in the pattern For having approximately even spacing between maxima A sketch of the intensity graph was also acceptable 1 point 1 point © 2006 The College Board. All rights reserved. Visit apcentral.collegeboard.com (for AP professionals) and www.collegeboard.com/apstudents (for students and parents). 10 AP® PHYSICS B 2006 SCORING GUIDELINES (Form B) Question 4 (continued) Distribution of points (c) (continued) (ii) 2 points For using an appropriate formula (or combination of formulas) and correctly substituting For example ml L xm ª d (1) 450 ¥ 10 -9 m (1.4 m ) xm ª 0.15 ¥ 10 -3 m For the correct answer x = 4.2 mm ( 1 point ) 1 point © 2006 The College Board. All rights reserved. Visit apcentral.collegeboard.com (for AP professionals) and www.collegeboard.com/apstudents (for students and parents). 11 AP® PHYSICS B 2006 SCORING GUIDELINES (Form B) Question 5 10 points total Distribution of points (a) (i) 2 points From the ideal gas law, PV T = a constant Points A and B are on the isothermal, so they are at the same temperature. Therefore, PBVB = PAVA PB 2V0 = PAV0 For the correct answer PB 1 = 2 PA For a correct justification (such as the reasoning shown above) 1 point 1 point (ii) 2 points Points C and B are at the same pressure. P P Therefore, C = B PA PA For the correct answer PC 1 = 2 PA For a correct justification (such as the reasoning shown above) 1 point 1 point (iii) 2 points Points A and B are on the isothermal, so they are at the same temperature. For the correct answer TB =1 TA For a correct justification (such as the reasoning shown above) 1 point 1 point © 2006 The College Board. All rights reserved. Visit apcentral.collegeboard.com (for AP professionals) and www.collegeboard.com/apstudents (for students and parents). 12 AP® PHYSICS B 2006 SCORING GUIDELINES (Form B) Question 5 (continued) Distribution of points (a) (continued) (iv) 2 points Points C and A are at the same volume. P T Therefore, from the ideal gas law C = C . PA TA PC 1 = , which was determined in part (ii) above 2 PA For the correct answer TC 1 = 2 TA For a correct justification (such as the reasoning shown above) (b) 1 point 1 point For a correct explanation Internal energy depends only on the temperature. Since step I is isothermal there is no change in temperature and thus no change in internal energy (c) 1 point 1 point 1 point For a correct explanation W = - P DV . In step III there is no change in volume, and thus no work done. 1 point © 2006 The College Board. All rights reserved. Visit apcentral.collegeboard.com (for AP professionals) and www.collegeboard.com/apstudents (for students and parents). 13 AP® PHYSICS B 2006 SCORING GUIDELINES (Form B) Question 6 10 points total (a) Distribution of points 1 point For a correct expression for kinetic energy K = mu 2 2 Note: This point was only awarded if no extraneous energy formulas were used. (b) 2 points For using the correct expression for de Broglie wavelength l=h p For the correct answer in terms of the given quantities l = h mu (c) 1 point 1 point 1 point 2 points For a correct expression for the total energy of the electron and positron Etotal = 2 mu 2 2 + mc 2 ( ) 1 point Can also add that since u << c , Etotal ª 2mc2 The two photons share this energy equally. For the correct answer E photon = mu 2 2 + mc 2 OR E photon ª mc 2 (d) 1 point 3 points For using the given expression for the photon energy E photon = hf 1 point For expressing the energy in terms of the wavelength f = c l so E photon = hc l 1 point Substituting the energy obtained in part (c) OR mu 2 2 + mc 2 = hc l mc 2 = hc l For the correct answer OR l = h m c l = 2 hc mu 2 + 2 mc 2 ( (e) 1 point ) 2 points For any indication that conservation of momentum applies For a correct explanation of why conservation of momentum requires two photons Example: since the total momentum of the electron and positron was zero, the total momentum of the products must be zero. Since a photon cannot have zero momentum, two photons traveling in opposite directions are required. Note: Only 1 point total was awarded for attempts to explain using Newton’s third law. 1 point 1 point © 2006 The College Board. All rights reserved. Visit apcentral.collegeboard.com (for AP professionals) and www.collegeboard.com/apstudents (for students and parents). 14 ...
View Full Document

This note was uploaded on 02/25/2010 for the course PHY 15166 taught by Professor Mr.donald during the Spring '10 term at 4.1.

Ask a homework question - tutors are online