20150930

Online reading assignment: energy conservation

Physics 205A, fall semester 2015
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.
"I did not understand most of it."

"The weight force of Earth on an object is a conservative force, as when this gravitational force does work against an object, removing its energy, it is able to store this energy, and return it to the object by later doing work on the object, therefore we talk about the increases or decreases in gravitational potential energy."

"The concept that energy cannot be created nor destroyed. It is only stored and transferred into different forms."

"Elastic potential energy: when a rubber band is stretched, there is a higher energy than when it is relaxed."

"There are conservative and nonconservative forces that can act on things. Elastic and gravitational potential energies are conservative. These can be used for mechanical or useful energy."

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 trying to grasp all of these concepts I'm not really aware of what I need to work on."

"I found most of it confusing."

"How to tell if gravitational potential energy is increasing or decreasing."

"Just please lecture on the important points in this section. Nothing is too confusing a long as it is properly explained."

"I don't fully understand about gravity being a conservative force, and where or how it stores energy."

For the woman moving upwards after being catapulted, her translational kinetic energy __________ while her gravitational potential energy __________.
decreases; increases.   ************************************ [36]
increases; decreases.   ***************** [17]
(Unsure/lost/guessing/help!)   ***** [5]

For the ball bearing being launched by the slingshot, its translational kinetic energy __________ while the elastic potential energy of the slingshot bands __________.
decreases; increases.   ****** [6]
increases; decreases.   ************************************************ [48]
(Unsure/lost/guessing/help!)   **** [4]

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. [65%]
Gravitational potential energy: decreases. [64%]
Elastic potential energy (of the bungee cords): increases. [59%]

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.   ********** [10]
her gravitational potential energy.   **************************** [28]
the elastic potential energy of the bungee cords.   ******** [8]
(Unsure/lost/guessing/help!)   ************ [12]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Please help. I think 'unsure/lost/guessing/help' is the #motto today."

"Gravitational potential energy and elastic potential energy are pretty straightforward."

"I would benefit from more examples of the energy conservation problems."

"Whew--a lot covered in these section, but will be ready to dive in and reinforce tomorrow."

"Uh...I dunno about these. I understand that if one type of energy increases, the others have to decrease to compensate (since energy cannot be created nor destroyed or something like that), but I will definitely need some explanation on these."

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