## 20140908

### Online reading assignment: vector components, projectile motion

Physics 205A, fall semester 2014
Cuesta College, San Luis Obispo, CA

Students have a 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 vector components and projectile 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.
"Vectors have a defined direction in space and magnitude. Scalars have magnitude but no direction in space. Projectile motion takes place in a vertical plane."

"Projectile motion is just like free fall with a non-zero horizontal component. The angle of the initial velocity is the angle of elevation and the path it takes is trajectory."

"We can use trigonometry to relate a vector to its x- and y- components. The use of trigonometry allows us to find many different unknowns using the Pythagorean theorem and sine, cosine, and tangent functions."

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.
"Why ax = 0 for projectile motion."

"The concept of trajectory is a little confusing, as far as what remains constant."

"I found a lot to do with the triangles and trigonometry to be somewhat confusing, can we go over some of the basics?"

Mark the level of your exposure to trigonometry (triangles, unit circles, inverse functions, Pythagorean theorem):
 None at all. ** [2] Slight. **** [4] Some. *********** [11] A fair amount. *************************** [27] A lot. *********** [16]

For all possible cases of an object during ideal projectile motion, its horizontal acceleration component ax must be:
 a positive value. *********** [11] zero. **************************** [28] a negative value. *** [3] (More than one of the above choices.) ************ [12] (Unsure/guessing/lost/help!) ****** [6]

For all possible cases of an object during ideal projectile motion, the distance traveled will be __________ to the magnitude of the displacement.
 less than. *** [3] equal to. ********** [10] greater than. ****************** [33] (More than one of the above choices.) ****** [6] (Unsure/guessing/lost/help!) ******** [8]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"On the quiz you gave us, it seems that one of the starred answers was wrong, problem #6 if I remember. Can we get some clarity on that?" (That was a really hard problem. I've posted a worked-out solution on my blog, which is also linked to from Twitter using the #CuestaPhys205A hashtag. #smh #studentfail #teacherfail #pointsforeveryone.)

"Please use examples when going over class content." (I am. And I will continue doing so. I've also been posting the whiteboard work on these examples on Twitter using our #CuestaPhys205A hashtag.)

"Can you please show the answers to the online questions? (I always post the answers on my blog just before class, but also link to them from Twitter using the #CuestaPhys205A hashtag.)

"Are these graded for correctness and completion?" (Primarily for completion. Just try your best, and if most of the students are having problems, then that informs me as to what to emphasize in class the next day.)

"Do we have to memorize all these formulas the textbook keeps giving?" (Not if they're provided on the quizzes and exams.)

"How are you doing as of late?" (I had an awesome adventure with Mrs. P-dog. How was your weekend?)