P-dog's blog: boring but important

20111017

Physics midterm question: horizontally and diagonally-pulled suitcases

Physics 205A Midterm 1, fall semester 2011
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Example 4.13

A suitcase is dragged across a floor either using a horizontal rope, or using a diagonal upwards rope. The floor is not frictionless. Discuss why there is less kinetic friction force on the diagonally upwards pulled suitcase. Explain your reasoning by using free-body diagram(s), the properties of friction, forces, and Newton's laws.

Solution and grading rubric:

p:
Correct. Discusses how (kinetic) friction force is proportional to the normal force exerted by the floor, and from Newton's first law, the vertical component of the applied force decreases the normal force (as they must together be equal to the weight) and thus the friction force is less than the first case, when then normal force is equal to the weight.
r:
As (p), but argument indirectly, weakly, or only by definition supports the statement to be proven, or has minor inconsistencies or loopholes.
t:
Nearly correct, but argument has conceptual errors, or is incomplete. May state that the vertical component of the applied force decreases the weight, such that the normal force (equal to the weight) is decreased, thus decreasing the kinetic friction force (proportional to the normal force).
v:
Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. At least some application of Newton's laws to compare kinetic friction forces using a free body diagram, with applied force decomposed into horizontal and vertical components.
x:
Implementation/application of ideas, but credit given for effort rather than merit. Appeals to less surface area as causing less friction.
y:
Irrelevant discussion/effectively blank.
z:
Blank.

Grading distribution:
Sections 70854, 70855
Exam code: midterm01w4Sh
p: 16 students
r: 0 students
t: 15 students
v: 19 students
x: 3 students
y: 0 students
z: 0 students

A sample "p" response (from student 3389), correctly applying Newton's first law along the vertical direction for both suitcases, but inadvertently labeling it "Newton's second law" for the second suitcase:

20111016

Education research: partial credit for multiple-choice questions (PCMC) student attitudes (fall semester 2011)

Starting fall semester 2008 and continuing through fall semester 2011, Cuesta College students taking Astronomy 210 (introductory astronomy) at Cuesta College, San Luis Obispo, CA have piloted the use of partial credit for multiple-choice (PCMC) questions.

During the ninth week of instruction (after taking four multiple-choice question quizzes, and a midterm with multiple-choice questions and short-answer/essay questions), students were given the opportunity to evaluate PCMC in an online "Partial Credit for Multiple-Choice (PCMC) Survey" hosted by SurveyMonkey.com.

These are the complete survey results. Analysis will be forthcoming after more data has been compiled from future semesters. Values for the mean and standard deviations are given next to the modal response category for each question. Note that the order of questions within sections II and III were randomly scrambled for each student.

Partial Credit for Multiple-Choice Survey
Cuesta College
Astronomy 210 fall semester 2011 sections 70158, 70160
(N = 48)

I. In order to receive credit for completing this survey, 
   first enter your first and last name below:
   ____


II. Recall that for this semester there is PCMC = "partial 
    credit for multiple choice," where you can get partial 
    credit even after circling a wrong answer, if you have 
    also eliminated an incorrect answer by marking it with 
    an "x."      
      Answer the following statements which may or may not 
    describe your beliefs about PCMC in this class.      
      Because of PCMC...

II.1 ...I read questions more carefully.
1. Strongly disagree      1 : *
2. Disagree               1 : *
3. Neutral               11 : ***********
4. Agree                 26 : **************************  [3.9 +/- 0.8]
5. Strongly agree         9 : *********
     
II.2 ...I spend more time taking a test. 
1. Strongly disagree      2 : **
2. Disagree               9 : *********
3. Neutral                8 : ********
4. Agree                 22 : **********************  [3.5 +/- 1.1]
5. Strongly agree         7 : *******

II.3 ...I feel more confident about circling a correct choice.
1. Strongly disagree      2 : **
2. Disagree               2 : **
3. Neutral               17 : *****************
4. Agree                 20 : ********************  [3.6 +/- 1.0]
5. Strongly agree         7 : *******

II.4 ...I look for incorrect choices before circling a correct choice.
1. Strongly disagree      3 : ***
2. Disagree               5 : *****
3. Neutral                8 : ********
4. Agree                 23 : ***********************  [3.6 +/- 1.1]
5. Strongly agree         9 : *********

III. Answer the following statements which may or may not describe 
     your beliefs about PCMC in this class.  

III.1 PCMC helped me answer test questions better.
1. Strongly disagree      0 : 
2. Disagree               0 : 
3. Neutral               19 : *******************
4. Agree                 20 : ********************  [3.8 +/- 0.7]
5. Strongly agree         9 : *********

III.2 I would recommend using PCMC in future semesters of this class.   
1. Strongly disagree      0 : 
2. Disagree               1 : *
3. Neutral                4 : ****
4. Agree                 20 : ********************
5. Strongly agree        23 : ***********************  [4.4 +/- 0.7]

III.3 Having PCMC a positive experience.
1. Strongly disagree      0 : 
2. Disagree               1 : *
3. Neutral                5 : *****
4. Agree                 24 : ************************  [4.2 +/- 0.7]
5. Strongly agree        18 : ******************

III.4 Using PCMC was difficult.    
1. Strongly disagree     20 : ********************
2. Disagree              21 : *********************  [1.8 +/- 3.0]
3. Neutral                5 : *****
4. Agree                  0 : 
5. Strongly agree         2 : **

III.5 I would identify incorrect choices even without PCMC.  
1. Strongly disagree      1 : *
2. Disagree               4 : ****
3. Neutral               14 : **************
4. Agree                 19 : *******************  [3.7 +/- 1.0]
5. Strongly agree        10 : **********

IV. (Optional.)  Please type in any comments you may have regarding 
    the use of PCMC in this class.

The following are all of the student responses to this question, verbatim and unedited.

"pcmc rocks!!!"

"it was very helpfull"

"I like that we are rewarded for being able to rule out an answer that is not correct. It reinforces test taking strategy that should be used in all multiple choice tests in any class."

"It's good."

"I think it's nice having PCMC. It helps with the proccess of elimination and it definitly is nice being able to get credit for picking out which answer is wrong on a test. I think that you should continue to use PCMC in the future."

"Keep PCMC"

"I really like using PCMC, it makes taking tests a little easier as well as making you feel less worried about whatever grade you get on the test."

"if you do a X and O on each probelm do you just get partial bacuse i market two or do you get full point if you mark both and they are both correct is it full creadit or partial because two are mark instead of just one beacuse i mark the incorrect and the correct on each probelm just in case ones is wrong then the other is ritghis that partial or full do you have to have both right to get full credit or just one answer to get full credit"

"I have never used PCMC before, and I would like to use it again. Thank you"

"II think PCMC gives the teacher a better undestanding of a students comprehension of the question."

"I Love PCMC!"

"You should put three right answers and one wrong that way, everyone has a 75% chance of getting the right answer!"

"I wish each question wasn't worth so many points (4 pts) especially when PCMC is worth .5 point."

"I think PCMC is good overall. It doesn't allow people to fluff off studying, however for those questions where a student is torn between two answers, it allows them to at least get some credit if they answer incorrectly. It also shows they at least have a rudamentry understanding of the concept."

"It was a nice way to get easy points and now that I think about it, it really did make me read the question answers more thoroughly."

"I think it does help a little with PCMC because even if the answer is wrong on a question, there is a possibility of obtaining some points for the problem given."

"Keep it going!"

"It was a nuetral expeiriance"

"it's a nice way to get points if i don't know the answer to a question."

"It's a Blessing"

"I like PCMC"

"I like the fact we can still get points for questions."

"I like the ability of getting partial points for questions."

"It like using a life line on who wants to be a millionaire...I love that show"

"I really enjoy the system"

"I think that this policy is one of the best I've ever heard of! It really gives us students a little extra push on being able to find the correct answer within some pretty hard material to learn. Thank you for allowing us the second chance!"

"Its th bees knees!!! Hey _____!"

"really like it!!"

"I usually look for obvious wrong answers, so this is great."

"PCMC!"

"I like it because it's almost like the 50/50 lifeline on Who Wants to Be a Millionaire. Sometimes when I find the one definite wrong answer, I look for more wrong answers if I'm not completely sure on a positive answer. Helps me narrow down choices."

"I like it. It's really helpful. Thanks."

"Just a quick reminder of its existence before each test would be helpful for us forgetful types."

"good stuff"

Education research: partial credit for multiple-choice questions (PCMC) student attitudes (fall semester 2008)

Education research: partial credit for multiple-choice questions (PCMC) bibliography

Astronomy quiz question: distance from apparent and absolute magnitudes

Astronomy 210 Quiz 4, fall semester 2011
Cuesta College, San Luis Obispo, CA

[Version 1]
Cygnus OB2-12 is a star that has an apparent magnitude m = +11.4 and an absolute magnitude M_V = −10.6. How far away is Cygnus OB2-12 from Earth?
(A) Much farther away than 10 parsecs.
(B) A little farther away than 10 parsecs.
(C) Exactly 10 parsecs away.
(D) Closer than 10 parsecs away.

Correct answer: (A).

Cygnus OB2-12 appears to be +11.4 as seen from its true distance from Earth, but when placed at the "fair" distance of 10 parsecs away, its becomes much brighter (−10.6). Thus it was brought much closer to Earth when moved to 10 parsecs, and was located much farther than 10 parsecs away from Earth.

Section 70158
Exam code: quiz04sIZ3
(A) : 17 students
(B) : 8 students
(C) : 0 students
(D) : 9 students

Success level: 48% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.89

[Version 2]
σ Sagittarii is a star that has an apparent magnitude m = +2.05 and an absolute magnitude M_V = -2.14. How far away is σ Sagittarii from Earth?
(A) Much farther away than 10 parsecs.
(B) A little farther away than 10 parsecs.
(C) Exactly 10 parsecs away.
(D) Closer than 10 parsecs away.

Correct answer: (A).

σ Sagittarii appears to be +2.05 as seen from its true distance from Earth, but when placed at the "fair" distance of 10 parsecs away, its becomes much brighter (-2.14). Thus it was brought much closer to Earth when moved to 10 parsecs, and was located much farther than 10 parsecs away from Earth.

Section 70160
Exam code: quiz04nuO6
(A) : 12 students
(B) : 10 students
(C) : 2 students
(D) : 0 students

Success level: 53% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.83

Astronomy quiz question: same size, but different temperature stars

Astronomy 210 Quiz 4, fall semester 2011
Cuesta College, San Luis Obispo, CA

[Version 1]
A(n) __________ has the same size as, but is cooler than a G0 supergiant.
(A) A5 supergiant.
(B) B0 main sequence star.
(C) M5 giant.
(D) G0 white dwarf.

Correct answer: (C).

Using an H-R diagram, the G0 white dwarf is much smaller than the G0 supergiant, and is the same temperature. The B0 main sequence star the same luminosity as the G0 supergiant, and is hotter than the G0 supergiant. The only stars that have the same size as a G0 supergiant are an A5 supergiant and an M5 giant. However, the A5 supergiant is hotter than the G0 supergiant, while the M5 giant is cooler than the G0 supergiant.

Section 70158
Exam code: quiz04sIZ3
(A) : 2 students
(B) : 8 students
(C) : 22 students
(D) : 5 students

Success level: 63% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.28

[Version 2]
A(n) __________ has the same size as, but is hotter than a G0 supergiant.
(A) A5 supergiant.
(B) B0 main sequence star.
(C) M5 giant.
(D) G0 white dwarf.

Correct answer: (A).

Using an H-R diagram, the G0 white dwarf is much smaller than the G0 supergiant, and is the same temperature. The B0 main sequence star the same luminosity as the G0 supergiant, and is hotter than the G0 supergiant. The only stars that have the same size as a G0 supergiant are an A5 supergiant and an M5 giant. However, the M5 giant is cooler than the G0 supergiant, while the A5 supergiant is hotter than the G0 supergiant.

Section 70160
Exam code: quiz04nuO6
(A) : 13 students
(B) : 5 students
(C) : 3 students
(D) : 3 students

Success level: 58% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.83

Astronomy quiz question: Wien's law

Astronomy 210 Quiz 4, fall semester 2011
Cuesta College, San Luis Obispo, CA

The ___________ of a star can be deduced by observing its color.
(A) distance.
(B) size.
(C) temperature.
(D) mass.

Correct answer: (C).

Section 70160
Exam code: quiz04nuO6
(A) : 1 student
(B) : 0 students
(C) : 22 students
(D) : 1 student

Success level: 92% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.17

Astronomy quiz archive: sun/spectra/star properties

Astronomy 210 Quiz 4, fall semester 2011
Cuesta College, San Luis Obispo, CA

Section 70158, version 1
Exam code: quiz04sIZ3

Section 70158

Quiz 4 results (max score = 40):
   0- 8.0 : **  [low = 7.5]
 8.5-16.0 : ******
16.5-24.0 : ****************  [mean = 20.9 +/- 6.7]
24.5-32.0 : ************
32.5-40.0 : *  [high = 36.5]

Section 71060, version 1
Exam code: quiz04nuO6

Section 71060

Quiz 4 results (max score = 40):
   0- 8.0 : *  [low = 4.0]
 8.5-16.0 : **
16.5-24.0 : ***
24.5-32.0 : ************  [mean = 26.8 +/- 8.6]
32.5-40.0 : ******  [high = 40.0]

Physics midterm problem: Washington Monument baseball catch

Physics 205A Midterm 1, fall semester 2011
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problem 3.47

Baseball player Charles "Gabby" Street, a catcher for the Washington Senators, was reported to have caught a baseball thrown from a window near the top of the Washington Monument on August 21, 1908 [*]. Assume that the baseball was initially thrown horizontally, and was caught at a horizontal distance of 6.0 m and a vertical distance of 160 m below from where it was thrown. What was the initial (horizontal) speed of the ball? Neglect air resistance. Show your and explain your reasoning using properties of projectile motion.

[*] Francis Stann, "Street's Ironic Monument," Baseball Digest, vol. 10, no. 4 (April 1951), pp. 29-30.

Solution and grading rubric:

p:
Correct. Determines the time t = 5.7 s for the baseball to fall (with no initial vertical velocity), and then solves for the initial horizontal velocity v_0x = x/t = 1.1 m/s. May either directly solve for t, or other equation(s) to first solve for the final vertical velocity v_y = –56 m/s.
r:
Nearly correct, but includes minor math errors. Uses quadratic equation coefficient a = –9.80 m/s² instead of –4.90 m/s², or x instead of y, or sets v_x = 0.
t:
Nearly correct, but approach has conceptual errors, and/or major/compounded math errors. Can at least solve for t or v_y.
v:
Implementation of right ideas, but in an inconsistent, incomplete, or unorganized manner. Some attempt at systematic use of kinematic equations for projectile motion.
x:
Implementation of ideas, but credit given for effort rather than merit. Use of angular kinematic equations, etc.
y:
Irrelevant discussion/effectively blank.
z:
Blank.

Grading distribution:
Sections 70854, 70855
Exam code: midterm01w4Sh
p: 35 students
r: 7 students
t: 2 students
v: 8 students
x: 1 student
y: 0 students
z: 0 students

A sample "p" response (from student 1123), solving for the final vertical velocity before ∆t:

Another sample "p" response (from student 3737), directly solving first for ∆t, with the additional baseball skills assessment of the person who released the ball from the Washington Monument:

20111015

Physics midterm problem: SmartCar wet pavement turn

Physics 205A Midterm 1, fall semester 2011
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problem 5.19, Comprehensive Problem 5.75

"Tiny U circle in a smart car"
Guy Smith
youtu.be/eO4KiKAk7kE

A SmartCar Pure Coupe (mass of 900 kg[*]) can turn around in a circle with a minimum radius of 4.4 m[**]. If the coefficient of static friction between tires and a wet parking lot is 0.20[***], what is the maximum possible speed for this turn on a flat, wet parking lot, without skidding? Show your work and explain your reasoning using a free body diagram, and the properties of forces, Newton's laws, and uniform circular motion.

[*] "Turning circle = 28.7 ft; ECE weight without driver = 1,808 lbs," smartusa.com/models/pure-coupe/specifications.aspx.
[**] "The size of a [turning] circle is actually its diameter, not its radius," wki.pe/Turning_radius.
[***] engineeringtoolbox.com/friction-coefficients-d_778.html.

Solution and grading rubric:

p:
Correct. Draws free-body diagram to illustrate that the normal force upwards must have the same magnitude as the weight force downwards, due to Newton's first law, and that the static friction force points inwards to satisfy Newton's second law for uniform circular motion (or these may be implicit in setting up N = m·g and µ_s·N = mv²/r equations). Solves for v..
r:
Nearly correct, but includes minor math errors. Correct numerical result, but no free body diagram or clear use of Newton's first law and Newton's second law, or free body diagram may include (fictitious) centrifugal forces.
t:
Nearly correct, but approach has conceptual errors, and/or major/compounded math errors.
v:
Implementation of right ideas, but in an inconsistent, incomplete, or unorganized manner. Some attempt at applying Newton's laws.
x:
Implementation of ideas, but credit given for effort rather than merit. Use of angular kinematic equations, etc.
y:
Irrelevant discussion/effectively blank.
z:
Blank.

Grading distribution:
Sections 70854, 70855
Exam code: midterm01w4Sh
p: 18 students
r: 8 students
t: 4 students
v: 12 students
x: 10 students
y: 0 students
z: 1 student

A sample "p" response (from student 3389):

20111014

Education research: college physics midterm statistics

Cuesta College Physics 205A (college physics, algebra-based, mandatory adjunct laboratory) students students take their first midterm on kinematics, Newton's laws, and circular motion in the eight week of instruction.

The midterm consists of five multiple-choice questions, two short-answer questions, and two worked-out problems, to be completed within 80 minutes (the length of a regularly-scheduled lecture).

Grading statistics:

Cuesta College
Physics 205A fall semester 2011 sections 70854, 70855 
Exam code: midterm01w4Sh
Midterm 1 results (N = 53, max score = 75):
 0-15 :   
16-30 : ******  [low = 25]
31-45 : *********
46-60 : *******************  [mean = 52.9 +/- 13.9]
61-75 : *******************  [high = 75]

The order in which students turned in their completed midterms was recorded, beginning approximately 20 minutes after starting, to 80 minutes after starting. With a linear regression r² value of 0.0644, there is no significant correlation between the completion order c turning on the midterm and resulting score S (S = -0.2342c + 59.181).