28 minutes to work on problems, then 30 minutes on the FRQ portion.
Tomorrow: Multiple choice portion.
3/3 AP: Solutions to momentum test review packet
Multiple choice
- d
- a (option: c if you say there is a slight increase in the kid’s momentum away from the sled and a slight increase in the sled’s
- c
- a
- b
- c
- b
- a
- c
- b
- c
- b
- d
- T
- T
- F
- T
- a
- a (both have the same momentum, but Speedy G has more kinetic energy, and it’s the energy that can break bones since energy can be lost, and this loss of energy is what damages the object it hits)
- c
- b
- a
- b
- b
- c
- d
- d
- e (oops, two 28s, second one is e as well)
- e
- b
- c, e
- c
- a
Written review
3/2 AP: Momentum review packet
Test will be on Wednesday. Work on the review packet today and tomorrow; if you have any questions about any of the problems, post them here.
Solutions to the packet will be posted tomorrow.
Typos in printed version
(These are corrected in the PDF version linked/shown on this page.)
- Caution, there are two #28s.
- # 20 should end with “… kinetic energy of the car and water in it.”
- first #28 (C) should read mv cos θ
File Name: 00411_Momentum-Review-1.pdf
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2/27 AP: Momentum practice problems
2/25 AP: Energy test review
Today we will be looking at the energy unit test, then continuing to work on momentum and collisions.
Momentum test on Friday.
2/21 AP: Identifying models in problem solving
Evaluating problems to determine models used.
Read problems 46-55.
Working in trios, you will be assigned one problem. For each problem:
- Draw sketch(s) and add labels for any information given.
- Your sketch will usually need a ‘before instant of collision’ sketch as well as and an ‘after instant of collision’ sketch.
- In some case you may need an additional sketch showing what happened after the instant of the collision.
Homework
Solve six of five of problems 46-55.
2/20 AP: 1D collision wrap-up
Here are the solutions to the homework problems, so you can check your work:
- #19: v f golf ball = 0.65 m/s
- #20: (a) v f rifle = 0.49 m/s; (b) v f man & rifle = 0.020 m/s
- #21: (a) v f girl = 1.15 m/s; (b) v f plank = 0.346 m/s opposite the girls motion
- #25: v f arrow = 1.67 m/s
- #27: (a) v f cars = 1.8 m/s; (b) K lost = 2.16×104 J
- #28: v i bullet = 529 m/s
- #29: height bullet & ball = 57 m
- #31: v f Gale & bro & sled = 15.6 m/s
Tomorrow we will look at collisions in two dimensions!
2/19 AP: More momentum problems.
It looks like I’ll be back on Thursday. Still a rough throat, but the doc thinks I’ll be ready by then. I’ll probably have a wireless mic so I don’t have to strain my voice 😊 .
You might also find these instruction helpful.
I hope to post some videos showing how to solve yesterday’s assigned problems, but here are a few others that might be helpful.
2/18 AP: Conservation of momentum book problems
Book reading/review
- Review 6.2 Conservation of Momentum, pages 166-168
- Read 6.3 Collisions, pages 168-175
- Pay particular attention to the Problem-Solving Strategy method described on page 173.
Problems (pages 182-184)
Remember that only when a collision is described as elastic can you use conservation of kinetic energy.
6.2 Conservation of momentum
Problems 19, 20, 21
6.3 Collisions & Glancing collisions
Problems 25, 27, 28, 29, 31
2/13 AP: p and K spreadsheet calculations
Today you will finish your spreadsheet calculations.
Remember, momentum is a vector, so some of your velocities will be negative. Be sure to include these, and that they match the relative directions of your carts.
- Start with one trial and:
- Use formulas in the spreadsheet to calculate p, K, Δ , %, etc.
- Once you have the trial with correct formulas, copy/paste those to all your other trials.
- For Δ in p and K, we always use (final-initial).
- For percent, we want to know the percent change, so use ( Δ / initial)
- Add some colors to make it easier to read
Averaging explosions calculations
Problem
Since we want to calculate percent as compared to the initial, and the initial p and K are zero, we can’t divide by the initial. Instead, use the following formula (all momentum values are the final values, since the originals are all zero)“
Solution
Rationale
Numerator: If momentum is conserved, then pa + pb should equal zero (one value being negative), so the numerator in our traditional change/original calculation would be zero.
Denominator: We would want the denominator to represent some value we are comparing to, so let’s chose the average of the two momenta…but since one is positive and the other is negative, we need to take the absolute value of each before averaging them.
And finally…
If your group was not able to collect any data, please use the following spreadsheet and save a copy for your group. bit.ly/VHSmomentum
Here’s a video about momentum and kinetic energy in car crashes for your enjoyment: