Online reading assignment: simple harmonic motion

Physics 205A, fall semester 2019
Cuesta College, San Luis Obispo, CA

Students have a bi-weekly online reading assignment (hosted by SurveyMonkey.com), where they answer questions based on reading their textbook, material covered in previous lectures, opinion questions, and/or asking (anonymous) questions or making (anonymous) comments. Full credit is given for completing the online reading assignment before next week's lecture, regardless if whether their answers are correct/incorrect. Selected results/questions/comments are addressed by the instructor at the start of the following lecture.

The following questions were asked on reading textbook chapters and previewing a presentation on simple harmonic motion.


Selected/edited responses are given below.

Describe what you understand from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically demonstrate your level of understanding.

"Simple harmonic motion is repeated motion back and forth, assuming no outside forces interact with the object, and that under ideal circumstances the motion repeats continuously. When graphed, Simple harmonic motion tends to be similar to a sine/cosine function."

"That the period T is the time it takes for an object in simple harmonic motion to complete one cycle. I also understand that the frequency is related to the period in that the frequency is the number of cycles of the motion per second and can used to find the hertz, or one cycle per second."

"That total energy conservation equals a constant because as KE translational increases then PE elastic will decrease. I also know simple pendulum period is determined by the length of the string which is why in the billiard ball example they all start to swing at different rates even though they are released at the same time."

"That springs have no kinetic energy and maximum potential energy at compression and fully stretched, while they have maximum kinetic energy and no potential energy at equilibrium."

"I don't think I understand anything in this section. I've re-read the section multiple times."

Describe what you found confusing from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically identify the concept(s) that you do not understand.

"The part that confuses me is putting it all together. But lecture will help with that."

"I didn't really understand the pendulum period/length stuff."

"I did not really understand the units of certain variables in some of the new functions like L."

"Do pendulum/mass-spring periods always use 2π in the equation?"

"The mass spring period is a little confusing, I feel as though I understand the basis of it. Essentially more mass means more time or T in the mass spring period. Also a weaker spring constant would mean T would be greater. I think."

"There weren't any major things I found confusing. However, it is helpful when we go over the math of the problems and how to sub things in."

"I just need this taught to me. I don't learn well from reading."

"I first was confused on when to use the mass-spring period equation and the energy conservation equation. But then I realized that the first is used when given time and the other when focusing on energy."

"The math in how to perform these examples and the wording in the book is very confusing."

"I understand the basics but I guess the only thing I find 'confusing' is how many formulas are introduced in this chapter. I feel like normally we focus on one or two. I hope you will clarify which ones we will be using primarily."

The total energy of a mass-spring system would have zero translational kinetic energy and all elastic potential energy at the:

origin (x = 0).	******* [7]
turnaround points (x = ±A).	************************************* [37]
(Both of the above choices.)	* [1]
(Neither of the above choices.)	[0]
(Unsure/lost/guessing/help!)	[0]

The total energy of a mass-spring system would have all translational kinetic energy and zero elastic potential energy at the:

origin (x = 0).	************************************* [37]
turnaround points (x = ±A).	****** [6]
(Both of the above choices.)	[0]
(Neither of the above choices.)	** [2]
(Unsure/lost/guessing/help!)	[0]

For these identical mass billiard balls hanging from strings of different lengths, the billiard balls hanging from shorter length strings have periods that are _________ the periods of the billiard balls hanging from longer length strings.

shorter than.	***************************************** [41]
equal to.	** [2]
longer than.	[0]
(Unsure/lost/guessing/help!)	** [2]

For the different mass riders on swings of the same lengths, the more massive rider has a period __________ the period of the less massive rider.

shorter than.	***** [5]
equal to.	************** [14]
longer than.	************************** [26]
(Unsure/lost/guessing/help!)	[0]

For the overloaded truck with a vertical oscillation period of approximately half a second, after dumping its load (thus decreasing the mass connected to the springs in its suspension) would __________ the period of oscillation.

decrease.	************************* [25]
have no affect on.	* [1]
increase.	*************** [15]
(Unsure/lost/guessing/help!)	**** [4]

For this mass connected to two springs, its springs weakening over time (decreasing its spring constant) would __________ the period of oscillation.

decrease.	********************** [22]
have no affect on.	**** [4]
increase.	*************** [15]
(Unsure/lost/guessing/help!)	**** [4]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"Go over these."

"I didn't understand the swing question, they have different masses but appear to be swinging the same." (Yes, that is exactly what you should be seeing.)

"How much more will we be working with springs and stuff?" (You'll have a lab on this later, where you tinker around with periods of pendulum and mass-spring systems.)

"Seems simple enough."

"I'm never going to understand physics."

"Life is really getting to me now."

"I can't believe it's already November :|"

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]

Online reading assignment: energy conservation

Physics 205A, fall semester 2019
Cuesta College, San Luis Obispo, CA

Students have a bi-weekly online reading assignment (hosted by SurveyMonkey.com), where they answer questions based on reading their textbook, material covered in previous lectures, opinion questions, and/or asking (anonymous) questions or making (anonymous) comments. Full credit is given for completing the online reading assignment before next week's lecture, regardless if whether their answers are correct/incorrect. Selected results/questions/comments are addressed by the instructor at the start of the following lecture.

The following questions were asked on reading textbook chapters and previewing a presentation on energy conservation.


Selected/edited responses are given below.

Describe what you understand from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically demonstrate your level of understanding.

"The easiest concept for me to understand from the reading and slide is the fact that translational kinetic energy is directly correlated to speed, in that if speed increases, so does translational kinetic energy."

"Gravitational potential energy is the energy that an object of mass has by its position in relation to the surface of Earth measured by the height of the object and an arbitrary zero level."

"I think gravitational potential energy is the easiest energy type to identify. If an object is 2 m off the ground then it has more gravitational potential energy than if the same object were 1 m off the ground."

"The gravitational force can do negative and positive work and that only the initial and final position should be considered when solving problems. This is also why it is considered a conservative force. Also, the greater the height, the greater gravitational potential energy is."

"A conservative force is not dependent on the path between start and finish points. Therefore, these types of forces also equate to zero work if the start and finish are the same."

"Conservative force is when the work done on an object is independent from the path taken between the initial and final heights, or when it does no net work on an object on a closed path. Nonconservative force is when the work done on an object moving between two points does depend on the path of motion, as we see with force of friction, air resistance, tension, etc."

"The basics of gravitational and elastic potential energy. And how they are combined with the change in translational kinetic energy in transfer balance equation."

"When a spring is pulled back it causes the energy to be stored and once released it shoots out."

"I have learned that elastic potential energy, translational kinetic energy and gravitational potential energy all play a part in non-conservative and conservative work. As the height of where an object is increases, so does its gravitational potential energy. As a slingshot is stretched back with a rock in the sling, the elastic potential energy increases. As it is fired off, the translational kinetic energy increases, and elastic potential energy decreases."

"This specific topic was kind of a blur, not gonna lie. I understand conservative forces and how how they can store energy and later retrieve without loss, and the opposite for nonconservative energy. That makes sense, but what doesn't is the application of information into the equations."

"Not much."

Describe what you found confusing from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically identify the concept(s) that you do not understand.

"I am a little unsure if the translational kinetic energy is simply increased as an object's movement or speed increases."

"Translational kinetic energy is difficult to comprehend on a practical level."

"Applying the equations to gravitational potential energy and elastic potential energy. Also need better clarification of conservative and non-conservative work."

"The transfer-balance equation and how to use it."

"I would like an example of using the transfer-balance equation in class because I am still confused on how to properly implement it into my problem-solving."

"I found the transfer-balance equation slightly confusing at first but then soon realized that its a total energy conservation equation. Other than that I did not find anything else confusing."

"I found it confusing to apply the certain types of energies to certain problems. For example, when do you use potential energy, kinetic energy, and/or mechanical energy? I understand the differences of the three. However, will a question on a test ask us to find one of these or a few of these or will we have to decide that based on the problem? "

For the woman moving upwards after being catapulted, her translational kinetic energy __________ while her gravitational potential energy __________.

decreases; increases.	*************************************** [39]
increases; decreases.	********* [9]
(Unsure/lost/guessing/help!)	* [1]

For the ball bearing being launched by the slingshot, its translational kinetic energy __________ while the elastic potential energy of the slingshot bands __________.

decreases; increases.	********** [10]
increases; decreases.	************************************** [38]
(Unsure/lost/guessing/help!)	* [1]

For the woman falling off the building starting from the edge of the roof to just before reaching her lowest point of descent, indicate the changes in each her of energy forms. (Only correct responses shown.)

Translational kinetic energy: increases. [80%]
Gravitational potential energy: decreases. [74%]
Elastic potential energy (of the bungee cords): increases. [76%]

For the woman falling off the building starting from the edge of the roof to just before reaching her lowest point of descent, the energy form that experienced the greatest amount of change (increase or decrease) was:

her translational kinetic energy.	************* [13]
her gravitational potential energy.	*************** [15]
the elastic potential energy of the bungee cords.	**************** [16]
(Unsure/lost/guessing/help!)	***** [5]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"How do we know when something is non-conservative and conservative?"

"For the examples above, they were cases of either an increase of kinetic energy and decrease of gravitational potential energy, or vice versa. Is it possible the have increase-increase or decrease-decrease?" (Only if there was (positive) work be done to add energy to the system, or (negative) work being done to remove energy from the system. Otherwise if there are only two types of energy and no work being transferred to/from the system, then an increase in one type of energy must be fed by a corresponding decrease in the other type of energy, and vice versa.)

"For the woman on the bungee swing, how are we supposed to know which energy experiences the greatest amount of change without numeric values?"

"Will there be a study guide for the midterm that's a little more structured on the key concepts we need to know? Or do we just have to shuffle through our quizzes and homework, etc.?" (Go through the list of example midterm questions on next week's announcements page. The idea is that the methods and concepts used to answer those examples is what you would need to apply to answer your upcoming midterm.)

"Having a hard time understanding the textbook, YouTube is my friend but also sometimes my enemy."

"Can we do an end of the year potluck?" (The final exam is basically a "knowledge potluck." Everyone should bring something.)

Physics quiz question: mass-spring translational kinetic energy

Physics 205A Quiz 6, fall semester 2018
Cuesta College, San Luis Obispo, CA

A 0.75 kg mass attached to a horizontal spring has a 2.0 s period of oscillation. Neglect friction and drag. The velocity versus time graph for this mass-spring system is shown at right. The earliest time that the mass will have its maximum translational kinetic energy is:
(A) 0 s.
(B) 0.5 s.
(C) 1.0 s.
(D) 1.5 s.

Correct answer (highlight to unhide): (B)

The translational kinetic energy of the mass-spring system will be at a maximum when the velocity v has its greatest magnitude (regardless of direction), which occurs at t = 0.5 s and t = 1.5 s.

Sections 70854, 70855
Exam code: quiz06POr7
(A) : 5 students
(B) : 38 students
(C) : 6 students
(D) : 3 students

Success level: 73%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.67

Online reading assignment: simple harmonic motion

Physics 205A, fall semester 2018
Cuesta College, San Luis Obispo, CA

Students have a bi-weekly online reading assignment (hosted by SurveyMonkey.com), where they answer questions based on reading their textbook, material covered in previous lectures, opinion questions, and/or asking (anonymous) questions or making (anonymous) comments. Full credit is given for completing the online reading assignment before next week's lecture, regardless if whether their answers are correct/incorrect. Selected results/questions/comments are addressed by the instructor at the start of the following lecture.

The following questions were asked on reading textbook chapters and previewing a presentation on simple harmonic motion.


Selected/edited responses are given below.

Describe what you understand from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically demonstrate your level of understanding.

"A period is the time for the mass to complete one cycle of motion."

"Simple harmonic motion is back-and-forth motion. I found it interesting that we can relate its motion to sine and cosine graphs and how the two are related."

"The simplest form of periodic motion is simple harmonic motion. The spring constant is labeled k in the equation, and the stiffer the spring, the greater the value for k. Force is not constant so velocity and acceleration are not constant and constant acceleration kinematic equations do not apply."

"Simple harmonic motion is a special type of periodic motion or oscillation motion where the restoring force is directly proportional to the displacement and acts in the direction opposite to that of displacement. For a simple pendulum, the period depends on the square root of the string length L and the gravitational acceleration g."

"Simple harmonic motion refers to the constant back-and-forth motion of an object (ignoring any outside external forces of course), where a position versus time graph will produce either a cosine or sine function. We can analyze this motion with energy conservation equations."

"For a greater mass, the period of a mass-spring system increases. Also, the harmonic motion can be illustrated with sine/cosine graphs."

"Shorter strings on a pendulum would have shorter periods."

"When talking about the conservation of energy it's important to understand that energy is always conserved, it never just disappears it always turns into a different form on energy, when looking at say a spring problem it's important to look at the position of the spring to determine what type of energy it has. For a pendulum the mass doesn't affect its period, rather it's all about the length of the string. For the period of oscillation the bigger the spring constant the smaller the period and the vice versa."

"In the energy conservation equation, the total of both translational energy and elastic potential energy must equal to a constant, because no energy is lost or gained from the outside world/surroundings."

"That in harmonic motion external forces are ignored, which means the system will never come to a stop (total mechanical motion will be constant)."

Describe what you found confusing from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically identify the concept(s) that you do not understand.

"I was confused about what moment an object would have no translational KE or no elastic PE. Changing spring strength was a little confusing on how it would effect the period."

"Going over these chapters I still feel uncomfortable with oscillation and would greatly appreciate more guidance in class."

"How translational kinetic energy changes when the object moves away from and to its equilibrium position."

"Mass has no effect on the period of a pendulum?"

"For the pendulum period, I just thought that maybe a bigger mass would cause it to have a shorter time period because it is more mass pulling it down."

"I don't understand how increasing the gravitational constant would decrease the period of a pendulum."

"Something that confused me at first was the heavier masses for a pendulum period. I thought the mass didn't affect the swing, but after looking closely at the video, it helped me understand it more."
"Trying to find the simple harmonic motion periods with the simple pendulums and mass springs. Mathematically why would the period be the square root of the length over the gravitational acceleration."
"I'm just confused on the spring constant. Is it given? I'm cornfused. Also maybe just confused about the statement 'even though the relative amounts of KE_tr and PE_elas may be different, their total must always equal the same constant amount.' I need a picture I think."

"Nothing was really confusing in the assigned reading, I understood the basics. Maybe just a review of the mass-spring periods."

"I felt like I understood most of the presentation. I don't currently have any questions, but I may after lecture."

The total energy of a mass-spring system would have zero translational kinetic energy and all elastic potential energy at the:

origin (x = 0).	************ [12]
turnaround points (x = ±A).	***************************** [29]
(Both of the above choices.)	* [1]
(Neither of the above choices.)	** [2]
(Unsure/lost/guessing/help!)	****** [6]

The total energy of a mass-spring system would have all translational kinetic energy and zero elastic potential energy at the:

origin (x = 0).	***************************** [29]
turnaround points (x = ±A).	*********** [11]
(Both of the above choices.)	[0]
(Neither of the above choices.)	**** [4]
(Unsure/lost/guessing/help!)	****** [6]

For these identical mass billiard balls hanging from strings of different lengths, the billiard balls hanging from shorter length strings have periods that are _________ the periods of the billiard balls hanging from longer length strings.

shorter than.	******************************************** [44]
equal to.	** [2]
longer than.	[0]
(Unsure/lost/guessing/help!)	**** [4]

For the different mass riders on swings of the same lengths, the more massive rider has a period __________ the period of the less massive rider.

shorter than.	****** [6]
equal to.	********* [9]
longer than.	***************************** [29]
(Unsure/lost/guessing/help!)	****** [6]

For the overloaded truck with a vertical oscillation period of approximately half a second, after dumping its load (thus decreasing the mass connected to the springs in its suspension) would __________ the period of oscillation.

decrease.	******************************** [32]
have no affect on.	[0]
increase.	********** [10]
(Unsure/lost/guessing/help!)	******** [8]

For this mass connected to two springs, its springs weakening over time (decreasing its spring constant) would __________ the period of oscillation.

decrease.	********************* [21]
have no affect on.	** [2]
increase.	******************** [20]
(Unsure/lost/guessing/help!)	******* [7]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"When you state that 'increasing the gravitational constant (by changing its location?) would decrease the time to complete one cycle of motion,' are you stating that the object is in a different altitude? or different planet with a different constant?" (Yes. In fact, timing a pendulum period at different locations can be used to determine variations in the gravitational constant.)

"I don't fully concentrate on newer material when I need to concentrate on older material. I wish I was able to, but I need to focus on what we are being quizzed on." (I still appreciate the effort in at least skimming the material we'll be introducing for this class after the quiz.)

"I didn't get to the reading tonight because I've been studying for other exams; my bad." (Good luck!)

"Mythbust this: does a golf ball travel farther if the club head is wet?" (Sounds like a great abstract. Send me the rest of this lab report when you find out.)

"This section was very confusing for me!"

Physics quiz question: shooting a more massive foam dart

Physics 205A Quiz 6, fall semester 2016
Cuesta College, San Luis Obispo, CA

"Nerf Recon CS-6"
Anima Kitty
flic.kr/p/4meXDZ

A 2008 NERF® N-Strike Recon CS-6 toy gun can be modeled as a compressed horizontal spring that is released to push against a standard 1.3×10^–3 kg foam dart, which speeds up from rest to a final speed of 16 m/s.[*][**][***] Ignore drag/friction.

A slightly more massive dart launched from this same Recon CS-6 toy gun will have __________ final speed compared to the standard 1.3×10^–3 kg dart.
(A) a slower.
(B) the same.
(C) a faster.
(D) (Not enough information given.)

[*] nerfhaven.com/forums/topic/23927-dart-mass-listing/
[**] nerfguns.net/mods/mod-kits/
[***] instructables.com/id/Streamline-Dart-Mod/

Correct answer (highlight to unhide): (B)

Starting with the energy balance equation:

W_nc = ∆KE_tr + ∆PE_grav + ∆PE_elas,

where W_nc = 0 (no external gains/losses of mechanical energy), and ∆PE_grav = 0 (as there is no change in elevation of the foam dart as it travels horizontally), such that:

0 = ∆KE_tr + ∆PE_elas,

0 = (1/2)·m·∆(v²) + (1/2)·k·∆(x²),

0 = (1/2)·m·(v_f² – v₀²) + (1/2)·k·(x_f² – x₀²).

With the initial parameters of v₀ = 0 (starting from rest) and the final parameter x_f = 0 (spring relaxed after releasing the foam dart), then:

0 = (1/2)·m·(v_f² – 0²) + (1/2)·k·(0² – x₀²),

0 = (1/2)·m·v_f² – (1/2)·k·x₀²,

(1/2)·k·x₀² = (1/2)·m·v_f²,

(k·x₀²)/m = v_f²,

and thus the final velocity of the foam dart is given by:

v_f = x₀·√(k/m).

Using a more massive foam dart in the same toy gun would increase m in the denominator of the square root quantity (while the spring constant k and the distance x₀ that is spring is compressed from equilibrium would be unchanged), and thus this would result in a slower final speed compared to the original less massive foam dart.

Sections 70854, 70855, 73320
Exam code: quiz06rn3T
(A) : 44 students
(B) : 8 students
(C) : 4 students
(D) : 0 students

Success level: 79%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.18

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]

Online reading assignment: energy conservation

Physics 205A, fall semester 2018
Cuesta College, San Luis Obispo, CA

Students have a bi-weekly online reading assignment (hosted by SurveyMonkey.com), where they answer questions based on reading their textbook, material covered in previous lectures, opinion questions, and/or asking (anonymous) questions or making (anonymous) comments. Full credit is given for completing the online reading assignment before next week's lecture, regardless if whether their answers are correct/incorrect. Selected results/questions/comments are addressed by the instructor at the start of the following lecture.

The following questions were asked on reading textbook chapters and previewing a presentation on energy conservation.


Selected/edited responses are given below.

Describe what you understand from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically demonstrate your level of understanding.

"The work equation helps a lot when calculating forces and makes a lot of sense as long as you are able to break down which numbers you are supposed to plug into each variable in the equation."

"That an object has higher potential energy when it is at a higher elevation. That there are two types of forces, conservative and non-conservative. For non-conservative force this relates to energy that cannot be regained, like energy loss due to friction on an object."

"Gravitational potential energy will increase the higher the object is because the formula for this is mass times gravity times height. So the higher an object is and more it’s fighting with gravity thus the more potential gravitational energy. Mechanical energy is the sum of potential and kinetic energy."

"Weight force of Earth on an object is a conservative force, does work AGAINST an object, removes energy, is able to store the energy, and return it to the object by later doing work on the object. Work against an object removes energy. kg·m²/s² = joules."

"What made sense to me from the presentation preview was the two conservative energies and how work done by those two forces can be stored or later removed without loss. With respect to gravitational potential energy, I understood that an object higher in elevation had more potential energy than an object on the ground."

"It's more important to look for the change of an energy rather than just the energy."

"It seems easier to work out the equations using the final minus initial method."

"Gravitational potential energy and the change in gravitational potential energy. I also understood balancing equations which is kind of similar like in chemistry."

"There are two (so far) types of 'stored' energy, elastic and gravitational. in an ideal environment, energy is 'conserved' because it is not lost in work (done by non-conservative forces)."

"A conservative force is one that doesn't matter the path of the object it would still end up in the same place with the same amount of work."

"Conservative forces are those that are exerted on or against and objects, removing its energy and storing it for use to do work on the object at a later time, unlike non-conservative forces where the energy against an object is lost or irreversibly converted to non-mechanical forms."

"I think I understand the difference between conservative and non-conservative forces pretty well. Conservative forces can be retained and returned, for example, if someone were jumping on a trampoline, when they come down for a jump, the trampoline acts against the person and slows them down to a stop, but that energy that was working against the person is later returned as the trampoline pushes the person back up into the air and the energy lost is returned."

Describe what you found confusing from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically identify the concept(s) that you do not understand.

"I found the work-energy theorem kind of confusing and would just need some more practice problems on them to fully understand it. We got a brief introduction to it last class, but it didn't stick all too well."

"I don't understand how to calculate these different types of energies."

"I understood most of this content well, but I would like to work through some example problems."

"I understand this material pretty well."

"Elastic potential energy. I am just confused by the spring strength and the stretch/crunch terms."

"What I do not understand is how gravity is a conservative energy. Isn't it acting on an object all the time so how can it be conservative?"

"Honestly the algebra of rearranging the equations tripped me up for a good 20-25 minutes. Also the differences in equations for conservative versus non-conservative forces."

"I found it difficult understanding what conservative and non-conservative forces mean; (I'm not sure if what I understand is correct)."

"Whether friction would be a conservative force or not."

"I was a little confused when I first read that an object has zero gravitational potential energy when it is on the ground and at higher elevations it has more and more. I was thinking of it backwards and now understand."

For the woman moving upwards after being catapulted, her translational kinetic energy __________ while her gravitational potential energy __________.

decreases; increases.	******************************** [32]
increases; decreases.	****** [6]
(Unsure/lost/guessing/help!)	*** [3]

For the ball bearing being launched by the slingshot, its translational kinetic energy __________ while the elastic potential energy of the slingshot bands __________.

decreases; increases.	******* [7]
increases; decreases.	***************************** [29]
(Unsure/lost/guessing/help!)	***** [5]

For the woman falling off the building starting from the edge of the roof to just before reaching her lowest point of descent, indicate the changes in each her of energy forms. (Only correct responses shown.)

Translational kinetic energy: increases. [54%]
Gravitational potential energy: decreases. [68%]
Elastic potential energy (of the bungee cords): increases. [73%]

For the woman falling off the building starting from the edge of the roof to just before reaching her lowest point of descent, the energy form that experienced the greatest amount of change (increase or decrease) was:

her translational kinetic energy.	****** [6]
her gravitational potential energy.	************* [13]
the elastic potential energy of the bungee cords.	*********** [11]
(Unsure/lost/guessing/help!)	*********** [11]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"The cat in the 'curling cat' video is amazing!"

"This last question of which force experienced the greatest amount of change for the woman falling off the building with bungee, shouldn't all three energy forms be experiencing the same amount of change? Or does the gravitational potential energy experience the greatest amount of change?" (Generally it is possible for three energy terms in the transfer-balance equation to experience the same amount of change (say, all increase the same amount, or all decrease the same amount), but only if there is a corresponding amount of work done on, or work done against the system. However for the woman falling off the building attached to the bungee cord, where we could assume that there is no work done by non-conservative forces, then the changes in all three energy terms (increases and decreases) must add up to zero, and so it won't be possible for all three of them to have the same amount of change, as there would need to be one decreasing energy and two increasing energies; or two decreasing energies and one increasing energy.)

"For the example with the bungee jumping women, the elastic potential energy decrease because it had its highest amount of potential energy when she was on top of the building and the gravitational potential energy decreased as she swings through the arc?" (Yes, as both the translational kinetic energy and elastic potential energy increase. Assuming that there is no work done by non-conservative forces, then the decrease in gravitational potential "feeds" the increases in translational kinetic energy and elastic potential energy.)

"I would benefit from some clarification of these examples of increasing and decreasing forms of energy."

"How to plug in information for the equations?"

"I need more time to read this section."

"If the two sliding boxes of equal mass/initial sliding speed slide across two different horizontal floor surfaces and come to a complete stop would have the same amount of work done on it by kinetic friction considering no changes in gravitational potential energy and elastic potential energy. But how is it that one box would travel farther, while the other box traveled less? Wouldn't there have to be some other force acting against the box that had the shorter sliding distance?" (No other horizontal force acts against these boxes other than the kinetic friction force. Both boxes have the same amount of work done against their motion by the kinetic friction force, but since work is force times displacement, the box that has the shortest sliding displacement must have a bigger kinetic friction force acting on it, and vice versa.)