## 20170906

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

Physics 205A, fall semester 2017
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.
"The chain of pain. I am starting to get how to use it when I am given certain information."

"Re-reading these sections helped me gain some understanding on these topics overall. It definitely gave me a greater understanding of applying the equations of kinematics but I still feel I could use some equations in class to go over."

"Acceleration is negative when it goes against the direction of velocity. Tangent lines touch the graph on one point."

"Since the velocity is a vector and the formula for the acceleration is the velocity over change in time, then Acceleration has also a magnitude and direction. Instantaneous acceleration will be a tangent line and average acceleration will be a chord line on a velocity versus time graph."

"There are four kinematic equations with multiple variables to make it possible to find a missing variable that we are interested in. If we are given all but one of the variables we can solve for the missing piece of the equation."

"When it comes to displacement it can be equal to distance traveled if there are no changes in the direction of motion. "

"Utilizing the given information/variables to select the best equation in determining an unknown variable."

"The different slopes are something that i understand. It makes sense to me that if it is between two point it is a chord slope and if it touches at one spot then it is a tangent slope."

"After re-reading the assignment, I was able to understand more about motion and the calculus equations. From the reading and online presentation, I was able to really focus on using constant acceleration equations."

"Moving around the chain of pain is straightforward, which is good seeing as there is a quiz soon."

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.
"Something that I'm still struggling with is figuring out what part of the chain of pain to use when I'm given information in a different format or wording than I'm used to. I think it would just take practice and a little more review during class."

"The thing I feel I'm not fully grasping is using the values of velocity or acceleration and applying them to a graph. I can understand how to read the graph usually but to come away with the desired value is difficult for me."

"Need some clarifications on the constant acceleration equations and how to use them."

"Because of the emphasis on memorization, this presentation wasn't too difficult to get the hang of."

"Although I understand the concept of the chart much more, I still get some confusion on applying the area. I just need a very quick explanation on when and how to use it. Is it always base×height?"

"I didn't find any of the information confusing. I did notice that finding the correct equation to use can be somewhat challenging, but writing-out all of the given variables and what you need to find helps immensely."

"Being able to pick out the variables in a word problem. However, that will probably get easier with more practice."

"How/when a chord can be a tangent line when a chord has to hit two points."

"The biggest concepts that I feel still confused by are when to use each kinematic equation for constant acceleration. It could totally just be that I really need to try to memorize it more, but I do understand you want to use the quantities that are given and find the equation that best suits it to find the missing/desired quantity. Maybe I am just overthinking it? Also, I still need to review the chain of pain better and follow the examples given in class. "

"Though I am confused by when to use the chain of pain and the kinematic equations for constant acceleration. I do understand the mathematics/rearranging of quantities to find the undetermined quantity."

"To be fully honest, I read the chapter two more times on top of the previous times a read it and I still do not understand it."

"How to solve for multiple unknown quantities, and would benefit from further explanation."

"I did not find anything confusing but appreciate the review."

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. [72%]
Initial horizontal velocity vx: known/given. [89%]
Final horizontal velocity v0x: known/given. [85%]
Horizontal acceleration ax: unknown/undetermined. [70%]
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. [87%]
Initial horizontal velocity vx: known/given. [41%]
Final horizontal velocity v0x: unknown/undetermined. [46%]
Horizontal acceleration ax: unknown/undetermined. [74%]
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. *  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. [76%]
Initial horizontal velocity vx: known/given. [76%]
Final horizontal velocity v0x: known/given. [85%]
Horizontal acceleration ax: unknown/undetermined. [63%]
Final time t (initial time t0 assumed to be 0): unknown/undetermined. [80%]

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.
"I think I understand how to calculate the differences between horizontal distance traveled and magnitude of the horizontal displacement, but not sure if I am exactly doing it correct/using the right numbers."

"Do you recommend just memorizing the chain of pain or not?" (If that works for you. If you have a different system, then by all means go for it.)

"How can we calculate for an object that does not move with constant acceleration?" (If acceleration is not constant, but its derivative ("jerk") is, then you would use a different set of constant jerk equations, say, where:

x = x0 + vx0t + (1/2)⋅ax0t2 + (1/6)⋅jt3,

and so on. #wut)

"Is there any difference between finding the area of the triangle below or above the slope?" (If the line is above the time axis, find the area "below the slope," down to the time axis. But if the line is below the time axis, then find the area "above the slope," up to the time axis.)

"How similar will these questions be to quiz/exam questions?" (My intent is to be very similar, as these were actual quiz questions from previous semesters.)

"I would benefit from further explanation on the selected topics. I do not learn well by self teaching from book material."

"The flipped class is confusing me."

"I do not understand this, I can't teach myself physics." (That's okay, as long as you're giving me a heads-up on specifically what you find confusing, so we can address this in class--even if it's everything.)

"For all three cases above I believe the distance is equal to the magnitude of horizontal displacement. They all seem to be going in a single direction without any turns or back tracks. It's weird to put 'equal to' three times in a row though so I am second-guessing myself." (Don't psych yourself out. Sometimes it is what it is.)

"Putting equations into other equations is a little confusing. Is there a simpler, or different, way to solve these equations?" (That's the way algebra works. #itiswhatitis)

"No comment." (You just did.)

"What's the best kind of musubi?" (SPAM musubi, of course.)