## 20180829

### Online reading assignment: free fall, vector components

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 previewing presentations on free fall and vector components.

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 have a a way better understanding of the free fall concept and how gravity affects these objects when thrown in the air and when falling. It was good to have a review of vectors and the trigonometry that goes with calculating them! I feel I have a clearer understanding about what was discussed in class on Monday."

"How to interpret the given equations and use them to solve for an unknown value in a word problem. I also understand that you can manipulate each equation to solve for a different unknown when needed."

"Cosine and sine trigonometric functions allow the x- and y-components of a vector to be calculated."

"How trigonometric functions relate the angles and sides of a right triangle."

"When an object is undergoing free fall, only the force of gravity is pulling on it, so it experiences the acceleration due to gravity, with a magnitude of 9.80 m/s2, and since the object is going in a downwards direction, it will always be a negative sign (if up is taken to be the positive vertical direction)."

"That we have to neglect drag on free fall."

"Sorry, I was very busy."

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.
"I'm not sure when to use the quadratic formula to find time. Also, a little discussion about vertical motion and signs/direction would be helpful."

"The equations. My brain has a harder time making sense of things when there are so many variables with different subscripts. It helps if I can write out a key with what each thing means."

"Some of the equations used were a bit confusing, mostly because I still need to learn the symbols of a lot of things we are learning."

"I would appreciate some review on free falling bodies and the different methods that come with the calculations. I have a better understanding of free falling bodies but i'm still not completely clear on the concept and i'd feel more confident if we discussed in class on Wednesday!"

"I need more explanation on how I assign the signs on the initial velocities for free fall."

"The vectors presentation was pretty confusing for me. I feel that I could use a better explanation."

"I found the vectors section confusing. I understand the steps/equations that are given and when to use them based on the info you have, but the trigonometric functions are unfamiliar to me."

"I don't quite understand the vectors. All the equations and things got to be a little much and I could use a little review in class."

"Nothing really confused me. I understood the basic concepts of everything."

"I'm sorry, P-dog."

Explain what assumptions are made about the amount of drag (air resistance) on an object said to be in free fall.
"When in free fall there is only the force of gravity; there is no air resistance."

"Gravity is the only force affecting an object in free fall."

"When dealing with idealized motion, objects in free fall are not thought to be affected by drag (air resistance)."

"There is no drag on an object said to be in free fall."

"That air resistance is negligible."

"During free fall, it states that in an idealized motion, the air resistance is neglected and the acceleration is nearly constant."

"I have no idea."

A boy steps off of a ledge (with no initial vertical velocity) and splashes into the water below.

Choose up to be the +y direction. The initial vertical velocity v0y has a __________ value.
 negative. ********* [9] zero. *********************************** [35] positive. *** [3] (Unsure/guessing/lost/help!) ** [2]
For the boy, the vertical distance traveled is __________ the magnitude of the vertical displacement.
 less than. ** [2] equal to. ***************************************** [41] greater than. **** [4] (Unsure/guessing/lost/help!) ** [2]

A ball is thrown and released downwards from the top of a building, and hits the ground below.

Choose up to be the +y direction. The initial vertical velocity v0y has a __________ value.
 negative. ********************************* [33] zero. ******** [8] positive. ****** [6] (Unsure/guessing/lost/help!) ** [2]
For the ball, the vertical distance traveled is __________ the magnitude of the vertical displacement.
 less than. ***** [5] equal to. ********************************* [33] greater than. ******** [8] (Unsure/guessing/lost/help!) *** [3]

A hat is thrown and released upwards into the air and lands on the grass below.

Choose up to be the +y direction. The initial vertical velocity v0y has a __________ value.
 negative. *** [3] zero. ******* [7] positive. ************************************ [36] (Unsure/guessing/lost/help!) *** [3]
For the hat, the vertical distance traveled is __________ the magnitude of the vertical displacement.
 less than. ** [2] equal to. ****** [6] greater than. ************************************ [36] (Unsure/guessing/lost/help!) ***** [5]

Mark the level of your exposure to trigonometry (triangles, unit circles, inverse functions, Pythagorean theorem):
 None at all. * [1] Slight. **** [4] Some. ***** [15] A fair amount. **************** [16] A lot. ************* [13]

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) [88%]
cos θ: (a/h) [90%]
tan θ: (o/a) [88%]
hypotenuse h length: √(o2 + a2) [86%]

Describe what mnemonic device (if any) you use to memorize the right-triangle trigonometric relationships.
"Soh-cah-toa."

The CAST rule is the way I memorize (positive) trigonometric functions."

"I do not remember them. "I do not have a mnemonic device to memorize any right-triangle trigonometric relationships."

"I just memorized the relations and studied each one because I had to know them."

"I do not use one currently but I would like to learn one."

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"when you throw a ball downwards the graph is considered to have a negative initial velocity correct? However would the vertical distance traveled be considered to be equal to the magnitude of vertical displacement? Since we don't have a positive initial velocity and the object is dropping from its initial to its final position without rising at any point, then that drop is considered a 'straight line' if you will, hence the vertical distance traveled should be equal to magnitude of vertical displacement right? (Yes, yes, yes.)

"If you could go over the answers for the questions regarding the vertical distance traveled that would be great."

"We need to go over distance vs displacement again, specifically when it is implied with these problems about free-fall." (We certainly will.)

"I know where we can see our quiz grades, but how do we keep track of the points we earn from quiz extra-credit, post-labs, reading assignments, and homework reports?" (All those points are also posted on the same page as the quiz scores. (Lab points will be posted separately, later.))

"Will we only be using the first quadrant?"

"Could you go into vector components a little more? The book makes it kind of confusing."