## 20180827

### Online reading assignment: constant acceleration equations of 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 reviewing a flipped class presentation on (constant acceleration) 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.
"Some of the basic differences between instantaneous velocity vs average velocity (same with acceleration). Average velocity puts into consideration the whole time scope from t0 = 0 s to the finish, whereas instantaneous uses small snippets of time and examines each small vector (hopefully I am explaining this correctly. Also the slopes and how to read/understand the graphs more this time around, and what the graph reflects about an object's movement. I realize that 'magnitude' reflects absolute value of a quantity."

"How to find velocity, acceleration and displacement through the use of calculus concepts pretty well. I took calculus in high school and a lot of the material is coming back to me which is great."

"That you have to choose which equation you use carefully to determine the correct unknown variable. I understand the correlations for the 'Chain of Pain,' and which operations should be used to calculate what is trying to be found."

"I'm beginning to understand the relationship between velocity, speed, displacement, and distance traveled a lot more than before. Although displacement and distance traveled can be the same, they can also be different if the movement of the object is not along a straight line. I'm also beginning to see that average speed connects to distance traveled whereas average velocity connects to displacement. Finding these connections among the variables has helped with my ability to problem solve and my overall understanding of the equations."

"I understand that when doing problems with kinematics, it is essential to write down the given information and work step by step in order to avoid errors. I also understand the four kinematic variables (x, vx, ax, and t) and their meaning."

"This was the same reading assignment as last time, which helped because I did not really understand the "chain of pain" until reading this chapter again. However, I have seemed to have a better grasp on the concept. I understand that you can find the distance traveled from a velocity graph by finding the are of the graph because the displacement is the same as distance traveled if the distance is all in one direction. I know you can find the average acceleration from a velocity graph by finding the chord slope."

"That in order to solve a problem, we should be able to determine which information is given to us and which isn't first. Then, figure out what equations to use, but actually using it in practice is confusing to me."

"That picking a random physics equation and trying to use it won't end well. I understand that in this class we will need to remember what equations to use and when to use them."

"I took a closer look at what all the variables stand for and it was a bit easier to read the equations."

"How to read the position versus time and the velocity versus time graphs. I think its a little bit easier to solve those problems actually instead of just when information is given."

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.
"Chords, tangents, and areas."

"I would like to go over how to use the chain of pain little bit more and brief overview the stuff is probable good for me."

"The differences between acceleration and velocity. Especially on which variables are used to calculate each one."

"Everything so far makes sense. The 'Chain of Pain' is becoming much clearer now as I spend more time with it and understand its components better."

"Honestly, the textbook is pretty confusing. The chapters assigned just confused me even further. Their use of examples to define something doesn't help explain what something is in the first place if you don't know what it is. How do you decide what equation to use?"

"The 'Chain of Pain' graphical relations flowchart makes sense when I am looking at it but it is very hard to remember/memorize. Hopefully more work with these types of problems will make me more efficient."

"Understanding graphs. Sometimes I get confused on which equations to use when given a graph to analyze. For instance, when to use the area below the curve versus a different type of equation. This confusion may have to do with the need for some more practice with graphs. I am however beginning to understand the equations themselves more which will probably slowly help with understanding the graphs."

"I do mostly understand the 'Chain of Pain' graph however, the symbols are still a bit confusing."

"Figuring out how to use the equations and knowing which one to use in a certain problem. I think during class it could be beneficial to learn how to analyze problems and figure out what information we already have and expand on the process of how to get what we want. I know we've already done this, but I have a hard time doing this with our assigned homework problems and problems from the book."

"Still not familiar with the equations used for finding values, especially what each variable represents. I need to review the definitions more."

"How to determine which equation you choose to determine the variable that is being asked to solve for."

"I think I'm okay."

Mark the level of your expertise in algebraically solving multiple equations for multiple unknowns.
 None at all. ****  Slight. ******  Some. **************  A fair amount. *****************  A lot. ********* "2012 Chrysler 300 - First Drive"
NRMA Motoring and Services
flic.kr/p/d1bozj

"The braking distance for a 2012 Chrysler 300C to slow down from 31 m/s to a complete stop is 50.3 m. Assume that the acceleration is constant as the car slows down to a stop."

From the statement of this problem, determine whether the values of these kinematic quantities are known/given or are unknown/undetermined (without solving the problem numerically).

(Only correct responses shown.)
Final horizontal position x (initial horizontal position x0 assumed to be 0): known/given. [88%]
Initial horizontal velocity vx: known/given. [82%]
Final horizontal velocity v0x: known/given. [84%]
Horizontal acceleration ax: unknown/undetermined. [72%]
Final time t (initial time t0 assumed to be 0): unknown/undetermined. [74%]

For the Chrysler 300C, the horizontal distance traveled is __________ the magnitude of the horizontal displacement.
 less than. ***  equal to. *********************************  greater than. ******  (Unsure/guessing/lost/help!) ******** "Leichtathletik WM 2009 Berlin"
André Zehetbauer
flic.kr/p/6RmNQn

"Jamaican sprinter Usain Bolt holds the world record for the 100 m sprint, covering that distance in 9.58 s in Berlin, 2009. Assume that his acceleration starting from rest to when he crosses the finish line is constant."

From the statement of this problem, determine whether the values of these kinematic quantities are known/given or are unknown/undetermined (without solving the problem numerically).

(Only correct responses shown.)
Final horizontal position x (initial horizontal position x0 assumed to be 0): known/given. [94%]
Initial horizontal velocity vx: known/given. [50%]
Final horizontal velocity v0x: unknown/undetermined. [56%]
Horizontal acceleration ax: unknown/undetermined. [74%]
Final time t (initial time t0 assumed to be 0): known/given. [96%]

For Usain Bolt, the horizontal distance traveled is __________ the magnitude of the horizontal displacement.
 less than.  equal to. **************************************  greater than. *****  (Unsure/guessing/lost/help!) ******* "6 kJ Portable Pneumatic Catapult"
UAV Factory
uavfactory.com/product/21

"A portable pneumatic catapult is able to launch a Penguin B unmanned aerial vehicle (UAV) from rest to a final speed of 23 m/s along a 4.0 m rail. Assume that the rail is horizontal, and that acceleration of the UAV starting from rest to when it is launched is constant."

From the statement of this problem, determine whether the values of these kinematic quantities are known/given or are unknown/undetermined (without solving the problem numerically).

(Only correct responses shown.)
Final horizontal position x (initial horizontal position x0 assumed to be 0): known/given. [74%]
Initial horizontal velocity vx: known/given. [82%]
Final horizontal velocity v0x: known/given. [82%]
Horizontal acceleration ax: unknown/undetermined. [70%]
Final time t (initial time t0 assumed to be 0): unknown/undetermined. [76%]

For the UAV, the horizontal distance traveled is __________ the magnitude of the horizontal displacement.
 less than. ***  equal to. ******************************  greater than. *****  (Unsure/guessing/lost/help!) ************ 

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Can we go over displacement vs distance again using the three examples you gave us for homework?"

"If something is traveling in a straight line and does not go backwards or turn right or left, is displacement equal to distance?" (Yes.)

"Can we use the kinematic equations to solve for distance traveled on a velocity versus time graph, or would you prefer we show how we found the area by using squares and triangles?" (Whichever method works best for you. I'll teach you both methods, but ultimately how you get your answer is your call.)

"Will you give kinematic equations to us on quizzes and exams, or do we need to memorize them?" (You are always given those equations, so don't memorize them. Instead concentrate on how they are to be used.)

"How do you decide which kinematic equation to use? And will you give these to us on tests/quizzes or do we need to memorize them?" (The "most useful" kinematic equation to use will depend on the information that you are given, and what you are being asked to solve for, which will be different for every particular problem.)

"Could we go through one of these problems in class?" (We will. Then you'll go through one of these problems on your own for problem-solving today, and then more for homework later.)

"I think I just need a bit more practice with identifying all the different variables in the problems, also being able to calculate the different variables as well."

"No comment or question today. Class is going well!"