Online reading assignment: impulse and momentum

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 a presentation on impulse and momentum.


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 concept of momentum and that its magnitude depends on both the mass and speed of an object, and how impulse is the product of the net force acting on an object and the duration of time that the net force acted on this object."

"That momentum is the mass of an object times the speed of that object and it is a vector because of the direction of that object's speed. Impulse is dependent on the average net force applied on an object and how long that force is applied."

"According to the impulse-momentum theorem, impulse causes a change in momentum."

"Both momentum and impulse are vector quantities. Momentum is the product of mass and velocity and change in momentum could be caused by impulse which is equal to the product of force and time."

"How to find the change in momentum. The change in momentum is the final momentum minus the initial momentum."

"It seemed like I was applying momentum and impulse the correct way during the examples but now going back over it I don't think I have a clear understanding of what either of them are."

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 found the impulse-momentum theorem a bit confusing."

"I didn't understand the concept of impulse, which is the product of the net force acting on an object and the duration of time that the net force acted on this object."

"I'm struggling to understand what exactly impulse and momentum are. More like what they do, and how to describe them in a problem."

"I don't understand why time plays a role in impulse and the change in momentum, but I think I understand now."

"Figuring out the signs (+ or –) when finding the change in momentum. I think it depends on what direction the object is going, but on some of the examples I was not sure what the signs would be."

"I honestly didn't find much in this chapter confusing. The subjects of momentum and impulse were not very difficult to me."

For the child hitting the tee ball with a bat, if the bat is swung such that it exerts the same net force on the tee ball for a longer time (by giving the bat more "follow-through"), the impulse on the tee ball will be __________, and the change in momentum of the tee ball will be:

less; less.	[0]
less; greater.	******* [7]
greater; less.	***** [5]
greater; greater.	***************************** [29]
(Unsure/lost/guessing/help!)	*** [3]

For this golf ball initially at rest, and then has a speed of 97 m/s (to the right) after being hit by a golf club, indicate the horizontal directions (+/– signs) for the various impulse-momentum theorem quantities. (Only correct responses shown.)

Golf ball's initial momentum p₀: no direction (0). [86%]
Golf ball's final momentum p_f: to the right (+). [86%]
Golf ball's initial-to-final change in momentum ∆p: to the right (+). [81%]
Golf club's impulse "J" on the golf ball: to the right (+). [70%]

For this F/A-18E-F Super Hornet initially at rest, and then has a speed of 74 m/s after being it is catapulted (to the left), indicate the horizontal directions (+/– signs) for these impulse-momentum theorem vectors. (Only correct responses shown.)

Super Hornet's initial momentum p₀: no direction (0). [86%]
Super Hornet's final momentum p_f: to the left (–). [39%]
Super Hornet's initial-to-final change in momentum ∆p: to the left (–). [36%]
Catapult's impulse "J" on the Super Hornet: to the left (–). [45%]

For this Ford Ranger, hitting a crash barrier with a speed of 11.0 m/s (to the right), and then rebounding (to the left) off the crash barrier with a speed of 2.2 m/s, indicate the directions (+/– signs) for the various impulse-momentum theorem quantities. (Only correct responses shown.)

Ford Ranger's initial momentum p₀: to the right (+). [86%]
Ford Ranger's final momentum p_f: to the left (–). [39%]
Ford Ranger's initial-to-final change in momentum ∆p: to the left (–). [36%]
Crash barrier's impulse "J" on the Ford Ranger: to the left (–). [45%]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"Can you go over the impulse-momentum theorem?"

"Is it possible to go over more conceptual aspects of this rather than examples? I'm having trouble figuring out from the reading what each of these concepts mean and I feel that I should know better what they are before I do example practice problems."

"Can you do more problems in class?"

"No questions on today's assignment, I think I got this so far!"

"I think I understood this stuff...after answering these questions, let's hope!"

"What?"

"Which is a scarier thought? That the human race is the most advanced form of life in the universe, or that we are mere amoebae compared to other life forms?"

"PANICKING!! WORRIED ABOUT MIDTERM!! Practice midterm NOT helpful. Sure we have the long weekend to study, but it will be difficult to ask you for help face-to-face (which is more effective than email)." (I will specifically go over what you need to know for the midterm, and target the Wednesday's review session such that ideally you can spend the long weekend how to apply the tools that you're given for the midterm, rather than trying to determine what tools are needed for the midterm.)