## 20150902

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

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 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.
"I learned about the importance of trigonometry in physics and how to use the sin, cos, tan, functions to determine certain angles and figure out how to solve problems with these features. I also learned about vectors and how they deal with both magnitude and direction."

"A projectile has no acceleration in the horizontal axis and that only gravity acts on it, and the path will be a parabola."

"It was interesting when the ball was shot upwards while the cart was moving horizontally and the ball landed to the cart. Projectile motion is just vertical free fall with a constant horizontal component."

"My level of understanding trigonometry is very basic. With a little bit of review on how to apply this to triangles in class I think I could have a better understanding."

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.
"How both the pool balls with different directions hit the ground at the same time."

"Just about all things velocity related."

"Nothing was confusing."

"Probably everything."

Mark the level of your exposure to trigonometry (triangles, unit circles, inverse functions, Pythagorean theorem):
 None at all. [0] Slight. *** [3] Some. ************* [13] A fair amount. ************************ [24] A lot. *********************** [23]

Indicate the following trigonometric relations between angle θ, the opposite leg o, the adjacent leg a, and hypotenuse h for a right triangle. (Assume that the angle θ is in the first quadrant: 0° ≤ θ ≤ 90°.)
(Only correct responses shown.)
sin θ: (o/h) [95%]
cos θ: (a/h) [94%]
tan θ: (o/a) [95%]
hypotenuse h length: √(o2 + a2) [97%]

Describe what mnemonic device (if any) you use to memorize the right-triangle trigonometric relationships.
"I don't remember. Oh! Is it SOH-CAH-TOA? One problem--I still don't remember what that stands for."

"SOH-CAH-TOA: sin = opp/hyp, cos = adj/hyp, tan = opp/adj. I learned it in ninth grade and it still stuck. There's a story that goes with it that I don't really remember though."

"I don't have one. Only my brain."

Indicate the initial velocity components for the (ideally) vertically-launched anvil.
(Only correct responses shown.)
v0x: 0 [84%]
v0y: positive [71%]

Indicate the initial velocity components for the car driven horizontally off the cliff.
(Only correct responses shown.)
v0x: positive [76%]
v0y: 0 [51%]

Indicate the initial velocity components for the car launched diagonally off the cliff.
(Only correct responses shown.)
v0x: positive [81%]
v0y: positive [62%]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"How can I best learn to understand 'physics talk' I'm finding it most difficult to even understand what questions are asking. Should I just be memorizing physics terminology?" (That's a necessary start. But there's much more past that, like concepts and applications.)

"Help! I get the concepts but applying them is not going well." (Okay, but you're nearly there--let's try to get you all the way there before the quiz.)

"I like triangles."

"Do you get to see a lot of things destroyed in physics?" (What is best in life? To crush your students, to see them driven before you, and to hear the lamentations of their parents.)

"What are you plans for Labor Day weekend?" (Hopefully Mrs. P-dog and I will be doing more of this.)