Impulse & Momentum 08

OPENING QUESTION: Tijana Boskovic is one of the all time great servers in volleyball. During the 2016 Olympics in Rio her serve was clocked 101 km/hr.

If her hand was in contact with the ball for 54 one-hundredths of a second, what force MUST she have exerted on the 270 gram volleyball to make it move that fast.

CALENDER: Let's review the upcoming work calendar Notice that I've moved back tomorrow's test.

WORDS O' THE DAY:

• Force (f=ma, measured in N)
• Momentum (p=mv, measured in kgm/s)
• Impulse (change in momentum = ∆p, also force exerted over time = F∆t therefore ∆p = F∆t)

WORK O' THE DAY:

The Physics Classroom Problem Set is HERE

I don't think we are *quite* ready for a test tomorrow. Towards that end we're going to do a little bit of ground and pound.... generally speaking I'm not a big fan of that, but this topic is heavily mathematical and we really do need some more practice.

So... with that in mind, please go to my website and go to the study guide section.

There is a rather massive number of problems to choose from on the Physics Classroom website. Most of those are very well put together, although a few are a bit odd... if you come to a problem that seems to not make so much sense, skip it and move on.

Also (and this is KEY), do NOT start at the top and work your way down. Find specific types of problems that give you indigestion and do those types of problems.

You're not going to want to do this, but if you are intent on learning this material, don't just do a full wolgemuthian, do an ANNOTATED full wolgemuthian. That means that you write little notes to yourself on the page as you go that explain WHY you did what you did. It can also be VERY helpful to write notes to yourself when you are stuck BEFORE you look at the answer... then go back and write additional annotations.

Problems in blue (29 - 32) are advanced and include topics from other units. If the other problems on this page are pretty comfy for you, give those a shot! Do NOT do those problems if you are struggling at all on any of the others...

NOTES: I'll add my comments here as students bring up questions, comments and/or concerns for individual problems:

The Physics Classroom Problem Set is HERE

 Problem #4 Basic This problem emphasizes the definition of momentum and the definition of impulse Problem # 7 Basic This problem emphasizes the relationship between momentum and impulse Problem #8 Basic This problem emphasizes the fact the the change in momentum occurs when velocity goes to zero. Problem # 10 Moderate This problem is sneaky. Read it carefully and the answers are obvious... however the author has deliberately added extraneous details. Problem #11 Moderate This problem emphasizes both the definition of impulse and how impulse can change the momentum of an object. In this case, multiple impulses each decrease the initial momentum of the object: Problem #15 Basic This problem will test your ability to setup initial conditions! Problem #18 Advanced This one emphasizes our definitions. The problem takes us by the hand for the first 3 steps and then encourages us to relate the change in momentum of the racket to the change in momentum of the ball (try that FIRST before checking my annotated solution is below) Problem #25 Sneaky Problem #25 requires us to *assume* (boo!) that either the masses of the two billiard balls are the same (just call them 'm' and they'll soon cancel out) or that this situation is an elastic collision. In an elastic collision the velocities are concerved so we don't need mass. Problem #28 NASTY! NASTY! NASTY! This problem is VERY complex and requires you to pull in information from previous units too. DO NOT attempt this problem unless you are VERY comfortable with the moderate and advanced probelms Problem #29 NASTY! NASTY! NASTY!