Physics quiz archive: rotations, torque, pressure, buoyancy, fluid flow

Physics 205A Quiz 5, fall semester 2019
Cuesta College, San Luis Obispo, CA
Sections 70854, 70855, version 1
Exam code: quiz05Gu1L



Sections 70854, 70855 results

0- 6 :	** [low = 6]
7-12 :	*********
13-18 :	***********
19-24 :	***************** [mean = 19.8 +/- 6.3]
25-30 :	************* [high = 27]

Physics quiz archive: rotations, torque, pressure, buoyancy, fluid flow

Physics 205A Quiz 5, fall semester 2018
Cuesta College, San Luis Obispo, CA
Sections 70854, 70855, version 1
Exam code: quiz05Ro74



Sections 70854, 70855 results

0- 6 :
7-12 :	******** [low = 9]
13-18 :	**************
19-24 :	************************* [mean = 19.6 +/- 5.2]
25-30 :	***** [high = 30]

Physics quiz archive: rotations, torque, pressure, buoyancy, fluid flow

Physics 205A Quiz 5, fall semester 2017
Cuesta College, San Luis Obispo, CA
Sections 70854, 70855, version 1
Exam code: quiz05nWaW



Sections 70854, 70855 results

0- 6 :
7-12 :	***** [low = 9]
13-18 :	***************
19-24 :	********************* [mean = 19.7 +/- 4.8]
25-30 :	***** [high = 27]

Physics quiz archive: rotations, torque, pressure, buoyancy, fluid flow

Physics 205A Quiz 5, fall semester 2016
Cuesta College, San Luis Obispo, CA
Sections 70854, 70855, 73320, version 1
Exam code: quiz05b0oM



Sections 70854, 70855, 73320 results

0- 6 :	*** [low = 6]
7-12 :	***********
13-18 :	************************* [mean = 16.6 +/- 6.0]
19-24 :	************
25-30 :	* [high = 30]

Physics quiz archive: rotations, torque, pressure, buoyancy, fluid flow

Physics 205A Quiz 5, fall semester 2015
Cuesta College, San Luis Obispo, CA
Sections 70854, 70855, 73320, version 1
Exam code: quiz05bL8D



Sections 70854, 70855, 73320 results

0- 6 :	** [low = 0]
7-12 :	****************
13-18 :	************************** [mean = 17.2 +/- 6.1]
19-24 :	**************
25-30 :	******** [high = 30]

Physics quiz archive: rotations, torque, pressure, buoyancy, fluid flow

Physics 205A Quiz 5, fall semester 2014
Cuesta College, San Luis Obispo, CA
Sections 70854, 70855, 73320, version 1
Exam code: quiz05mRp4



Sections 70854, 70855, 73320 results

0- 6 :	*** [low = 6]
7-12 :	*****************
13-18 :	************************* [mean = 16.5 +/- 5.7]
19-24 :	**************
25-30 :	***** [high = 30]

Physics quiz archive: rotations, torque, pressure, buoyancy, fluid flow

Physics 205A Quiz 5, fall semester 2013
Cuesta College, San Luis Obispo, CA
Sections 70854, 70855, 73320, version 1
Exam code: quiz05LuF7



Sections 70854, 70855, 73320 results

0- 6 :
7-12 :	************ [low = 12]
13-18 :	*********************** [mean = 18.4 +/- 4.9]
19-24 :	**********************
25-30 :	**** [high = 30]

Physics quiz archive: rotations, torque, pressure, buoyancy, fluid flow

Physics 205A Quiz 5, fall semester 2012
Cuesta College, San Luis Obispo, CA
Sections 70854, 70855, version 1
Exam code: quiz05L4mN



Sections 70854, 70855 results

0- 6 :	***** [low = 6]
7-12 :	*************
13-18 :	****************** [mean = 16.0 +/- 5.7]
19-24 :	***************
25-30 :	* [high = 30]

Physics quiz archive: rotations, torque, pressure, fluid flow

Physics 205A Quiz 5, fall semester 2011
Cuesta College, San Luis Obispo, CA
Sections 70854, 70855, version 1


Sections 70854, 70855 results
Exam code: quiz05t0rQ

0- 6 : *  [low = 6]
 7-12 : ***************
13-18 : **********************  [mean = 16.8 +/- 5.2]
19-24 : *********
25-30 : ****  [high = 30]

Physics midterm problem: inelastic rotational collision

Physics 205A Midterm 2, Fall Semester 2008
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 1/e, Problem 8.76

[20 points.] A 0.500 kg point mass is dropped onto a disk rotating at 4.00 rad/s that has a mass of 0.700 kg and a radius of 0.150 m. The point mass eventually rotates with the disk at a distance of 0.100 m from the axis. What is the final kinetic energy of the disk and point mass system? Show your work and explain your reasoning.

Solution and grading rubric:

• p = 20/20:
  Correct. Applies conservation of angular momentum to find the final angular velocity of the disk and point mass system; and then calculates the change in initial and final rotational kinetic energies in this inelastic rotational collision.
  
• r = 16/20:
  Nearly correct, but includes minor math errors.
  
• t = 12/20:
  Nearly correct, but approach has conceptual errors, and/or major/compounded math errors. Some attempt at applying conservation of angular momentum before evaluating the final kinetic energy.
  
• v = 8/20:
  Implementation of right ideas, but in an inconsistent, incomplete, or unorganized manner. Applies kinetic energy conservation to find final rotational kinetic energy, even though this is an inelastic rotational collision (as seen in lab), and if it were elastic, the final rotational kinetic energy would be exactly equal to the initial kinetic energy.
  
• x = 4/20:
  Implementation of ideas, but credit given for effort rather than merit.
  
• y = 2/20:
  Irrelevant discussion/effectively blank.
  
• z = 0/20:
  Blank.
  

Grading distribution:
Sections 70854, 70855
p: 1 student
r: 3 students
t: 3 students
v: 31 students
x: 3 students
y: 0 students
z: 2 students

A sample of the sole "p" response, applying angular momentum conservation to find the final angular velocity of the point mass and disk system, and then calculating the final (rotational) kinetic energy of this system (from student 0215):
A sample "t" response (from student 0420), with an attmempt to calculate the final kinetic energy of the system, but with a realization that the final angular velocity is not yet determined:

Physics midterm problem: disk rolling uphill

Physics 5A Midterm 2, Spring Semester 2008
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 1/e, Problem 8.62

[20 points.] A solid disk of mass 1.90 kg and radius 0.0500 m rolls without slipping along a horizontal surface with a translational speed of 0.240 m/s. (The rotational inertia of a disk is given by (1/2)*M*R^2.) It comes to an incline that makes an angle of 35.0 degrees with the horizontal surface. Neglecting energy losses due to friction, to what height above the horizontal surface does the disk rise on the incline? Show your work and explain your reasoning.


Solution and grading rubric:

• p = 20/20:
  Correct. Recognizes that W_nc = 0, such that when the disk has reached its highest height, all of its K_tr and K_rot has gone into U_grav. Writes out an energy balance equation 0 = delta(K_rot) + delta(K_tr) + delta(U_grav) and solves for y_f = 0.00441 m; or solves for K_tr,i and K_rot,i separately, then sets K_tot,i = K_tr,i + K_rot,i = U_grav,f to solve for y_f. Note that since the disk rolls without slipping, w_i = v_i/R.
  
• r = 16/20:
  Nearly correct, but includes minor math errors. Applies rolling without slipping condition, and recognizes both K_rot and K_tr must be accounted for separately in energy conservation.
  
• t = 12/20:
  Nearly correct, but approach has conceptual errors, and/or major/compounded math errors. Attempts to apply energy conservation, but one missing energy term out of K_rot, K_tr, or U_grav.
  
• v = 8/20:
  Implementation of right ideas, but in an inconsistent, incomplete, or unorganized manner. Some attempt at finding I = (1/2)*m*R^2, energy terms, Newton's laws, or applying angular momentum conservation.
  
• x = 4/20:
  Implementation of ideas, but credit given for effort rather than merit.
  
• y = 2/20:
  Irrelevant discussion/effectively blank.
  
• z = 0/20:
  Blank.
  

Grading distribution:
p: 4 students
r: 9 students
t: 12 students
v: 9 students
x: 1 student
y: 1 student
z: 0 students

A sample of a "p" response (from student 1125) is shown below:

A sample of a "t" response (from student 1239) that calculates both K_rot and K_tr, but only applies K_tr to U_grav in energy conservation:

Another "t" response sample (from student 7137) that applies only K_rot to U_grav in energy conservation:

One more "t" response (from student 1337) that also applies only K_rot to U_grav in energy conservation, with additional editorial comments:

Physics clicker question: empty can derby

Physics 5A, Fall Semester 2007
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 1/e, Conceptual Example 8.12

"All Disks Roll the Same," 1Q1035.mov
University of Minnesota, School of Physics & Astronomy
http://groups.physics.umn.edu/demo/mechanics/1Q1035.html

Students were asked the following clicker question (Classroom Performance System, einstruction.com) near the end of their learning cycle:

A V-8 can and a Diet Pepsi can (both empty) are placed at the top of an inclined plane, and are released such that they begin to roll down at the same time. (This experiment is set-up, but not yet demonstrated yet for the students until after answers have been compiled.)

[0.6 participation points.] Which empty can do you think will reach downhill first?
(A) V-8 can.
(B) Soda can.
(C) (They will reach the bottom of the slope at approximately the same time.)
(D) (I'm lost, and don't know how to answer this.)

Sections 0906, 0907
(A) : 11 students
(B) : 21 students
(C) : 5 students
(D) : 0 students

Correct answer: (C)

The energy conservation equation for a rolling ring (which approximates an empty beverage can) is:

0 = (1/2)*m*v_f^2 + (1/2)*I*w_f^2 + M*g*h,

where I = m*R^2, such that:

v_f = sqrt(g*h).

Thus both cans will have the same speed as they reach the bottom of the inclined plane, which can plausibly be reasoned to mean that they reach the bottom at the same time.

Physics clicker question: falling stick derby

Physics 5A, Fall Semester 2007
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 1/e, Comprehensive Problems 8.97, 8.98

"Falling Meter Sticks--Scaling," 1Q2060.mov
University of Minnesota, School of Physics & Astronomy
http://groups.physics.umn.edu/demo/mechanics/1Q2060.html

Students were asked the following clicker question (Classroom Performance System, einstruction.com) near the end of their learning cycle:

A 1-m stick and a 2-m stick are held vertically upright, and are released such that they begin to fall over at the same time. (This experiment is set-up, but not yet demonstrated yet for the students until after answers have been compiled.)

[0.6 participation points.] Which stick do you think will fall and hit the ground first?
(A) 1 m stick.
(B) 2 m stick.
(C) (They will hit the ground at approximately the same time.)
(D) (I'm lost, and don't know how to answer this.)

Sections 0906, 0907
(A) : 10 students
(B) : 7 students
(C) : 17 students
(D) : 1 student

Correct answer: (A)

The energy conservation equation for a falling stick is:

0 = (1/2)*I*w_f^2 + M*g*(L/2),

where I = (1/3)*M*L^2, such that:

w_f = sqrt(3*g/L).

Thus the shorter stick will have the faster speed as it hits the ground, which can plausibly be reasoned to be the stick that will reach the ground first, before the longer stick does.