Physics quiz archive: energy conservation, momentum conservation

Physics 205A Quiz 4, fall semester 2019
Cuesta College, San Luis Obispo, CA
Sections 70854, 70855
Exam code: quiz04JuR4



Sections 70854, 70855 results

0- 6 :	** [low = 6]
7-12 :	****
13-18 :	*******
19-24 :	********************** [mean = 21.9 +/- 6.1]
25-30 :	***************** [high = 30]

Physics quiz archive: energy conservation, momentum conservation

Physics 205A Quiz 4, fall semester 2018
Cuesta College, San Luis Obispo, CA
Sections 70854, 70855, version 1
Exam code: quiz04W3rK



Sections 70854, 70855 results

0- 6 :	* [low = 3]
7-12 :	********
13-18 :	**************
19-24 :	****************** [mean = 19.6 +/- 6.4]
25-30 :	********** [high = 30]

Physics quiz archive: energy conservation, momentum conservation

Physics 205A Quiz 4, fall semester 2017
Cuesta College, San Luis Obispo, CA
Sections 70854, 70855, version 1
Exam code: quiz04w33N



Sections 70854, 70855 results

0- 6 :
7-12 :	***** [low = 9]
13-18 :	****************
19-24 :	**************** [mean = 20.8 +/- 5.7]
25-30 :	*********** [high = 30]

Physics quiz archive: energy conservation, momentum conservation

Physics 205A Quiz 4, fall semester 2016
Cuesta College, San Luis Obispo, CA
Sections 70854, 70855, 73320, version 1
Exam code: quiz04th1R



Sections 70854, 70855, 73320 results

0- 6 :
7-12 :	**** [low = 9]
13-18 :	****************
19-24 :	*********************** [mean = 20.5 +/- 4.8]
25-30 :	******** [high = 27]

Physics quiz archive: energy conservation, momentum conservation

Physics 205A Quiz 4, fall semester 2015
Cuesta College, San Luis Obispo, CA
Sections 70854, 70855, 73320, version 1
Exam code: quiz04w04K



Sections 70854, 70855, 73320 results

0- 6 :	** [low = 6]
7-12 :	*******************
13-18 :	************************
19-24 :	****************************** [mean = 18.1 +/- 5.6]
25-30 :	*** [high = 30]

Physics quiz archive: energy conservation, momentum conservation

Physics 205A Quiz 4, fall semester 2014
Cuesta College, San Luis Obispo, CA
Sections 70854, 70855, 73320, version 1
Exam code: quiz04w3Rc



Sections 70854, 70855, 73320 results

0- 6 :	**** [low = 3]
7-12 :	********
13-18 :	******************
19-24 :	************************ [mean = 19.5 +/- 6.6]
25-30 :	*********** [high = 30]

Collision type flowchart

"Collision type flowchart"
http://flic.kr/p/o8oHFG
Originally uploaded by Waifer X

Flowchart by Cuesta College Physical Sciences Division instructor Dr. Patrick M. Len.

Physics quiz archive: energy conservation, momentum conservation

Physics 205A Quiz 4, fall semester 2013
Cuesta College, San Luis Obispo, CA
Sections 70854, 70855, 73320, version 1
Exam code: quiz04iSs5



Sections 70854, 70855, 73320 results

0- 6 :	** [low = 6]
7-12 :	***********
13-18 :	************************* [mean = 18.6 +/- 6.0]
19-24 :	******************
25-30 :	********** [high = 30]

Physics quiz archive: energy conservation, momentum conservation

Physics 205A Quiz 4, fall semester 2012
Cuesta College, San Luis Obispo, CA
Sections 70854, 70855, version 1
Exam code: quiz04Bmw3



Sections 70854, 70855 results

0- 6 :
7-12 :	******** [low = 9]
13-18 :	**********
19-24 :	****************** [mean = 21.3 +/- 6.0]
25-30 :	**************** [high = 30]

Physics quiz archive: energy conservation, momentum conservation

Physics 205A Quiz 4, fall semester 2011
Cuesta College, San Luis Obispo, CA
Sections 70854, 70855, version 1

Sections 70854, 70855 results
Exam code: quiz04iMpL

 0- 6 : **  [low = 6]
 7-12 : *****
13-18 : ******************
19-24 : ******************  [mean = 19.4 +/- 5.5]
25-30 : ********  [high = 30]

Collision flowchart

"Collision Flowchart," Patrick M. Len
October 17, 2008

Flowchart detailing the decision tree in determining which conservation laws apply to a particular type of collision.

Rearview train

Rearview Train, by pvictory
Worth1000.com
Amazing Reflections and Shadows contest

1. The train may appear closer than it actually is.
2. A perfectly inelastic collision is imminent.

Lolcat: feline collision

"clunk!" by ridemonke
icanhascheezburger.com
March 27, 2007

Physics 8A learning goal Q8.5

Whether or not the cats rebound from each other or not, momentum would still be conserved, provided that the collision was very brief, and/or that external impulses are negligible.

These cats were apparently posed and photographed from above while sleeping, and not actually photographed while in mid-collision.

Physics clicker questions: bullet into block sequence

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

Cf. Giambattista/Richardson/Richardson, Physics, 1/e, Problem 7.44

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

Object 1 = 0.020 kg bullet
Object 2 = 2.00 kg block
i = bullet before hitting block, block still stationary
f = just after bullet embedded into block, but before any sliding actually takes place

[0.6 participation points.] What is conserved for the process i→f?
(A) Momentum.
(B) Kinetic energy.
(C) Energy, with non-conservative work being done.
(D) (More than one of the above choices apply.)
(E) (Nothing is conserved.)
(F) (I'm lost, and don't know how to answer this.)

Sections 0906, 0907
(A) : 25 students
(B) : 3 students
(C) : 1 students
(D) : 7 students
(E) : 0 students
(F) : 0 students

Correct answer: (A)

Since there are no external horizontal impulses, momentum is conserved, such that v_12,f = (m_1*v_1,i)/(m_1 + m2). However, since there is deformation with no rebound and separation in this perfectly inelastic collision, kinetic energy is not conserved.

f = just after bullet embedded into block, but before any sliding actually takes place
ff = after block (with bullet inside) comes to a rest because of kinetic friction

[0.6 participation points.] What is conserved for the process f→ff?
(A) Momentum.
(B) Kinetic energy.
(C) Energy, with non-conservative work being done.
(D) (More than one of the above choices apply.)
(E) (Nothing is conserved.)
(F) (I'm lost, and don't know how to answer this.)

Sections 0906, 0907
(A) : 4 students
(B) : 9 students
(C) : 8 students
(D) : 8 students
(E) : 5 students
(F) : 1 students

Correct answer: (C)

Friction causes a horizontal impulse on the block (with embedded bullet), and thus momentum is not conserved. Friction also does work on the block/bullet, thus kinetic energy is not conserved, but energy is conserved if the non-conservative work done by friction is accounted for.

W_nc = delta(K_12),
-mu_k*(m_1 + m_2)*g*delta_x = (1/2)*(m_1 + m_2)*((v_12,f)^2 - 0).

Physics clicker questions: kinetic energy-momentum sequence

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

Cf. Giambattista/Richardson/Richardson, Physics, 1/e, Problem 7.7

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

Mass of (bowling?) ball = 5.0 kg

[0.6 participation points.] The ball is initially at rest, and then you push it such that it has a final speed of 3.0 m/s in the +x direction. What was the change in kinetic energy of the ball?
(A) –23 J.
(B) –15 J.
(C) 0 J.
(D) +15 J.
(E) +23 J.
(F) (I'm lost, and don't know how to answer this.)

Sections 0906, 0907
(A) : 1 student
(B) : 1 student
(C) : 1 student
(D) : 9 students
(E) : 22 students

Correct answer: (E)

[0.6 participation points.] What was the change in momentum of the ball?
(A) –23 kg*m/s.
(B) –15 kg*m/s.
(C) 0 kg*m/s.
(D) +15 kg*m/s.
(E) +23 kg*m/s.
(F) (I'm lost, and don't know how to answer this.)

Sections 0906, 0907
(A) : 0 students
(B) : 0 students
(C) : 0 students
(D) : 32 students
(E) : 2 students
(F) : 0 students

Correct answer: (D)

So far, so good--students seem to understand how to calculate changes in kinetic energy, and changes in momentum, especially when the initial velocity is zero.

---

Mass of (bowling) ball = 5.0 kg

[0.6 participation points.] The ball is moving with a speed of 3.0 m/s in the +x direction, and then hits a wall and bounces back with the same speed in the –x direction. What was the change in kinetic energy of the ball?
(A) –23 J.
(B) –15 J.
(C) 0 J.
(D) +15 J.
(E) +23 J.
(F) (I'm lost, and don't know how to answer this.)

Sections 0906, 0907
(A) : 1 student
(B) : 2 students
(C) : 25 students
(D) : 0 students
(E) : 5 students
(F) : 0 students

Correct answer: (C)

The final and initial speed is the same, so there is no change in kinetic energy.

[0.6 participation points.] What was the change in momentum of the ball?
(A) –23 kg*m/s.
(B) –15 kg*m/s.
(C) 0 kg*m/s.
(D) +15 kg*m/s.
(E) +23 kg*m/s.
(F) (I'm lost, and don't know how to answer this.)

Sections 0906, 0907
(A) : 27 student
(B) : 2 students
(C) : 5 students
(D) : 0 students
(E) : 0 students
(F) : 0 students

Correct answer: (A)

The final velocity is negative, and the initial velocity is positive, such that the change in momentum (the impulse) points in the -x direction. (Note that a negative change in kinetic energy corresponds to a decrease in speed; a negative change in momentum corresponds to the -x direction.)