## 20160829

### Online reading assignment: constant acceleration equations of motion

Physics 205A, fall semester 2016
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 the 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.
"With the explanations from last class about these same sections, I understand the equations we are supposed to use to find acceleration, velocity, etc., pretty well. The 'chain of pain' definitely helps a lot when it comes to graphs."

"After re-reading the textbook and reviewing the presentation, the content I understand most is probably the slide on calculus relations. I really like calculus so as soon as that connection was made to the physics equations, I actually understood it more. Plus, with calculus being a familiar lesson rather than foreign, I was more confident when doing the homework problems."

"The equations of kinematics are used when assuming that initial displacement is zero, initial time is zero and acceleration is constant. An object is decelerating when the acceleration vector points opposite the velocity vector."

"I already had read these sections before, but rereading it over again really made it make more sense. I can now visualize the situation more then before and make sense of the calculations."

"When solving for velocity, acceleration, or time there are several things you need to do. You need to identify all of the variables and figure out which one you are solving for, which ones are unknown and which ones are given or assumed to be known. Once you figure this out, you select the equation you will you use and solve for the unknown values."

"The concept of acceleration and deceleration was simple for me. It is easy to understand that acceleration and velocity will have opposite vectors when you decelerate because the object is slowing down but still continuing to move forward."

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.
"From just doing the reading the previous time I was very confused on how to find the velocity and such from just looking at a graph, but the 'chain of pain' helped clear that confusion up for me."

"The constant acceleration equations--I am not quite sure where they are derived from and what equation to use for what set of information given. Reviewing the homework problems assigned in the blog helped because it breaks it down step by step but I am still confused on how to identify what equation to use."

"Remembering which type of slope is calculated off of which type of graph."

"How the textbook explains concepts can be confusing. Once I think about it and look at it the concepts in a different way it makes more sense."

"I did not find much information about chord slopes and tangent slopes but after reviewing in class it is a simple concept."

"Doing the calculations in class really cleared up the confusion for me. Although knowing what one to use is still a little difficult. I think a little more practice with them will help."

"I didn't really find anything confusing, but I need to study the chain of pain a bit more and commit it to memory. Overall a pretty straightforward section."

"What I found confusing was simply manipulating the equations for the correct variable. In addition to this, it was difficult knowing which variables were known or 'assumed' to be known."

"The deciphering of the word problems into their respective formulas. For some of these problems it is difficult to pick out all the givens and unknowns and which formula to use."

"Something I am still struggling with is the kinematic equations and how to use them. I am having trouble discerning which variable goes with each number."

Mark the level of your expertise in algebraically solving multiple equations for multiple unknowns.
 None at all. * [1] Slight. *** [3] Some. ************** [14] A fair amount. ******************** [20] A lot. ***** [5]

"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. [72%]
Initial horizontal velocity vx: known/given. [84%]
Final horizontal velocity v0x: known/given. [79%]
Horizontal acceleration ax: unknown/undetermined. [79%]
Final time t (initial time t0 assumed to be 0): unknown/undetermined. [70%]

For the Chrysler 300C, the horizontal distance traveled is __________ the magnitude of the horizontal displacement.
 less than. * [1] equal to. ************************************ [36] greater than. *** [3] (Unsure/guessing/lost/help!) *** [3]

"Leichtathletik WM 2009 Berlin"
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. [93%]
Initial horizontal velocity vx: known/given. [54%]
Final horizontal velocity v0x: unknown/undetermined. [54%]
Horizontal acceleration ax: unknown/undetermined. [81%]
Final time t (initial time t0 assumed to be 0): known/given. [93%]

For Usain Bolt, the horizontal distance traveled is __________ the magnitude of the horizontal displacement.
 less than. * [1] equal to. *********************************** [35] greater than. ** [2] (Unsure/guessing/lost/help!) ** [2]

"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. [65%]
Initial horizontal velocity vx: known/given. [81%]
Final horizontal velocity v0x: known/given. [84%]
Horizontal acceleration ax: unknown/undetermined. [63%]
Final time t (initial time t0 assumed to be 0): unknown/undetermined. [86%]

For the UAV, the horizontal distance traveled is __________ the magnitude of the horizontal displacement.
 less than. *** [3] equal to. ********************** [22] greater than. ******* [7] (Unsure/guessing/lost/help!) *********** [11]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Please please review the answers to these questions in class if there is time!" (We'll go through some of these in class, but you can also look up the answers to these on this blog, via the #CuestaPhys205A hashtag on Twitter.)

"When using kinematic equations, does the equation always have to be set equal to the variable being solved for? Or can you plug in values and then solve for the variable?" (Either way should work fine, but I'm old school in thinking that it would be easier to algebraically solve for the variable first, and then plug in numbers.)

"On a quiz or test, when we are given a graph along with a question, will it be made clear whether we use the 'chain of pain' to answer it, or some other method?" (That would ultimately be your choice, but the 'chain of pain' should tell you what to do.)

"Wouldn't the horizontal distance traveled in all these questions be the same as the magnitude of horizontal displacement?" (Yes, because for each case, there was only motion in one direction only, and no back-and-forth motion.)

"The blog says that we will be given the equations on the exams: (a) is this still true, (b) is it true for quizzes as well?" ((a) Yes, and (b) yes.)

"I would like to see these homework questions worked out on the board if possible." (Yes, yes we can.)