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Unformatted text preview: AP® Physics B
2005 Scoring Guidelines
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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 freeresponse 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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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 bestfit line, but it was
needed for part (d) and was graded in that part. (d) 4 points
For drawing a reasonable bestfit 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.
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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.
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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.
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 Spring '10
 mr.donald
 Physics

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