Goals: SWBAT...
1. solve conservation of momentum problems in one-dimension
2. recognize the conditions under which momentum is conserved
3. solve conservation of momentum problems in two-dimensions
WARM-UP
1. This is a 2-D thought problem. No calculations necessary.
One blue billiard ball (mass, 0.1kg) is rolling horizontally at 2.5m/s across a table. It strikes a stationary red billiard ball (same mass), and after the collision, the red ball rolls away at an angle of 80* above the horizontal. Which of the following angles makes the most sense for the blue ball?
a/ 10* b/30* c/60* d/80* e/98 Degrees
Draw a sketch of the collision, similar to that on page 241
2. A 1-D problem. Carmen and Judi dock a canoe. 80.0-kg Carmen moves forward at 4.0 m/s as she leaves the canoe. At what speed and in what direction do the canoe and Judi move if their combined mass is 115 kg?
CLASSWORK
1. Conditions for Conservation of Momentum
If necessary, review the rules from page 236-7. Key words: Closed/Open; Isolated/Not Isolated
Could you use the conservation of momentum equation for the following problems? If no, why?
A. two balls on a flat table strike each other. One falls off the side of the table.
B. two balls on a flat table strike each other. They roll on the table, and don't fall off.
C. two balls on a flat table strike each other. A fan is blowing near the end of the table, and makes the second ball roll faster.
2. While watching the following (http://www.flippingphysics.com/2d-momentum.html) answer/do the following to build your understanding of 2-D problem solving
1. List the given info, and sketch the problem
2. Why does Mr. P show the cardinal directions (compass rose)?
3. How do B, B, and B break the velocity of Disc 1 into components?
4. Write the equations you'll use to solve. Include x and y subscripts if necessary
5. Solve for one component, then the other.
6. Elastic or inelastic? Why?
HOMEWORK
Finish up the answers to Classwork #2 above
Review Example #4 pg 242.
Solve pg 243 #22
Complete any late labs
#Goals: SWBAT...
1. ... review the basic components of "Work" & "Power"
2. ... solve basic work and power problems
WARM-UP:
1. When the brakes are applied in a car, which direction is the car's acceleration relative to it's motion?
2. Would the work done by the brakes in the above example be positive or negative work?
3. Find the work done on a 2.5kg encyclopedia that is raised by hand at a constant velocity, from the floor to a height of 2.0m.
Hint: You'll need to find the force applied by the lifting hand. Keep in mind that Newton's 3rd Law and the force from gravity are the concepts you need to use to find the applied force...
CLASSWORK:
1. Review our lesson from last class on Work and Power, by completing the "Think" section here: https://ed.ted.com/on/5bau54uF (If you need to see the video again, here's the link: https://vimeo.com/158272704)
2. How do we find the work on a shopping cart?
A. Brainstorm:
- What information would you need to solve the problem?
- Which equation(s) would you use?
- What are the forces on the cart? (draw an FBD)
B. Solve the problem http://www.flippingphysics.com/work-problem.html. Copy the solutions into your notes.
A nice write-up of the solution is here: http://www.flippingphysics.com/uploads/2/1/1/0/21103672/0137_lecture_notes_-_introductory_work_problem.pdf
3. Warm-Up Check
HOMEWORK:
1. Try some simple work problems:
pg 261 # 1 & 2
pg 262 #4