DAY 76
#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...
4. If it takes you 2 seconds to raise the book, how much power did you generate?
CLASSWORK:
1. Review of question #9 from your Ted ED HW & #2 from the book HW
2. Practice
pg 261 #3
3. Power Lab
Info Gathering/Reading. Read the lab on page 274-275
create a google doc and share it with my tch account.
Answer the following questions at the top of your doc
1. what is the question?
2. what will you have to do?
3. what data will you need to collect?
Hypothesis
Data Collection
04/27/17: Your google doc should currently have:
- names
- date
- title
- data table (similar to page 275) with weight, time, height data entered
4. Solving work problems in 2-D (save for next class)
Example
Practice pg 262 4 & 5
Homework: due Monday
A. Fill in the Power Lab as specified above in bold "Your google doc should currently have".
B. Do you know how to solve 2-D (x and y component) Work problems?
Complete the following by watching the video (link below) and find out :-)
1. What is the purpose of having Bobby 'translate' the problem as Billy reads it?
Do you do this? Should you?
2. Is Mr. P pushing the cart with a horizontal force, vertical force, or a combination of the two?
3. What is the unknown?
4. Draw the FBD
5. (Tatev, this should answer your question) For everyone, do you need to break the forces into their components? Why/Why not?
6. At 3:40, Mr. P is staring at the board, waiting for Billy, Bobby, and Bo to figure out the mistake. What is he waiting for them to discover?
7. What determines if the Work is positive or negative?
8. Theta is the angle between ______ and ______?
9. Does the normal force do work on the cart? Force from gravity?
Video LINK
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
#Goals: SWBAT...
1. ... collect data for Conservation of Energy Lab
2. ... review concepts of KE and PE
3. ... solve an potential energy problem
WARM-UP:
Read the paragraph on pg 291 on Elastic Potential Energy.
Elastic Potential Energy
When the string on the bow shown in Figure 11-7 is pulled, work is done on the bow, storing energy in it. Thus, the energy of the system increases. Identify the system as the bow, the arrow, and Earth. When the string and arrow are released, energy is changed into kinetic energy. The stored energy in the pulled string is called elastic potential energy, which is often stored in rubber balls, rubber bands, slingshots, and trampolines.
Energy also can be stored in the bending of an object. When stiff metal or bamboo poles were used in pole-vaulting, the poles did not bend easily. Little work was done on the poles, and consequently, the poles did not store much potential energy. Since flexible fiberglass poles were introduced, however, record pole-vaulting heights have soared.
Then solve #9 from page 292. See the example next to the whiteboard for help.
9. Elastic Potential Energy You get a spring-loaded toy pistol ready to fire by compressing the spring. The elastic potential energy of the spring pushes the rubber dart out of the pistol. You use the toy pistol to shoot the dart straight up. Draw bar graphs that describe the forms of energy present in the following instances.
a. The dart is pushed into the gun barrel, thereby compressing the spring.
b. The spring expands and the dart leaves the gun barrel after the trigger is pulled.
c. The dart reaches the top of its flight.
CLASSWORK:
1. Finish collecting lab data. You have 20 min. Labs are due Monday.
2. Read pg 285-289.
Create three questions and answers per person.
At least one question must be from pg 286-287; and one from pg 288-289.
3. Table of Friends:
NAME: SYMBOL EQUATION
Work
Kinetic Energy
Potential Energy
Elastic Energy
HOMEWORK:
1. Watch: http://www.flippingphysics.com/intro-peg.html
A. Defining Gravitational Potential Energy
B. Where is Zero Line #1
C. Where is Zero Line #2
D. Where is Zero Line #3
E. Where are the typical locations of the zero line? List them all...
F. What are the units for Gravitational Potential Energy? Copy the calculation for how Mr. P determines the units...