Ap07 physics b form b sg - College Board

AP? Physics B 2007 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.

? 2007 The College Board. All rights reserved. College Board, Advanced Placement Program, AP, AP Central, SAT, and the acorn logo are registered trademarks of the College Board. PSAT/NMSQT is a registered trademark of the College Board and National Merit Scholarship Corporation. Permission to use copyrighted College Board materials may be requested online at: inquiry/cbpermit.html. Visit the College Board on the Web: . AP Central is the official online home for the AP Program: apcentral..

AP? PHYSICS B (Form B) 2007 SCORING GUIDELINES General Notes About 2007 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 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. However, when students are asked to derive and 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. For a description of the use of such terms as "derive" and "calculate" on the exams, and what is expected for each, see "The Free-Response SectionsStudent Presentation" in the AP Physics Course Description .

4. The scoring guidelines typically show numerical results using the value g = 9.8 m s2 , but use of 10 m s2 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.

? 2007 The College Board. All rights reserved. Visit apcentral. (for AP professionals) and apstudents (for AP students and parents).

15 points total

(a)

4 points

AP? PHYSICS B 2007 SCORING GUIDELINES (Form B)

Question 1

Distribution of points

For each of the forces above with arrow correctly drawn and labeled, 1 point was awarded Notes: The force vector T could be shown in component form or as one force, but not both. For extraneous forces, 1 point was deducted.

4 points

(b)

4 points

? Fy = 0

N + T sin q - mg = 0

For a correct force equation N = mg - T sin q

For calculating the mg term correctly For calculating the T sinq term correctly

( ) N = (15 kg + 5 kg) 9.8 m s2 - (55 N)sin 20

For the correct numerical answer with units

N = 177 N (181 N if g = 10 m s2 is used)

1 point 1 point 1 point

1 point

(c)

3 points

? Fx = ma

For a correct Newton's second law equation involving horizontal forces T cosq - f = ma

a

=

T cosq m

-

f

For the correct relationship between the frictional and normal forces

f = mN

For correct calculation of the frictional force using the value of N from part (b)

f = (0.22)(177 N) = 38.9 N (39.8 N if g = 10 m s2 is used)

a

=

(55

N)cos20 -

20 kg

38.9

N

a = 0.64 m s2 ( 0.59 m s2 if g = 10 m s2 is used)

1 point

1 point 1 point

? 2007 The College Board. All rights reserved. Visit apcentral. (for AP professionals) and apstudents (for students and parents).

AP? PHYSICS B 2007 SCORING GUIDELINES (Form B)

Question 1 (continued)

(d)

2 points

For the correct work equation

W = (T cosq) d

For substituting the correct displacement

W = (55 N)cos20(7.0 m)

W = 360 J

(e)

2 points

Distribution of points

1 point 1 point

For each section of the graph correctly drawn as above, 1 point was awarded. Note: The second point was awarded only if the change at tr was abrupt.

2 points

? 2007 The College Board. All rights reserved. Visit apcentral. (for AP professionals) and apstudents (for students and parents).

10 points total

(a) (i) 2 points

AP? PHYSICS B 2007 SCORING GUIDELINES (Form B)

Question 2

Distribution of points

For at least two correct electric field lines in the right directions For the lines going through the entire Region I from top to bottom Note: A single line going from top to bottom could earn a maximum of 1 point.

(ii) 2 points

For either of the first two equations below quB = qE u=E B

u = (4800 N C) (0.12 T)

u = 4.0 ? 104 m s For the correct answer with units

(b)

2 points

quB

=

mu2 r

For the correct equation for the radius

r

=

mu qB

For correct substitutions consistent with the answer to (a)(ii)

( )( ) 6.68 ? 10-26 kg 4.0 ? 104 m s

r=

( ) 3.2 ? 10-19 C (0.12 T)

r = 0.070 m

1 point 1 point 1 point

1 point

1 point 1 point

? 2007 The College Board. All rights reserved. Visit apcentral. (for AP professionals) and apstudents (for students and parents).

 ................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download