DAY 66
#Goals: SWBAT...
1. ...review the basic components of "Work" & "Power"
2. ...solve work and power problems
3. ...calculate the power output of a person climbing stairs
WARM-UP:
1. What object(s) are these kids doing work on as they climb the stairs?
2. A rock climber wears a 7.5kg backpack while scaling a cliff. After 30.0 min, the climber is 8.2 m above the starting point.
A. How much work does the climber do on the backpack?
B. If the climber weighs 645 N, how much work does she do lifting herself and the backpack?
C. What is the average power developed by the climber? (recall the equation for power from yesterday - Power=Work/Time, where time is in seconds, and the work done on the object is the energy added to or removed from the object)
CLASSWORK:
1. HW Review
2. 066A: Power Practice Problems
- solve 9-13 on page 264
- LINK: https://drive.google.com/file/d/0B31ORq_bI3-VbEFBTERVc1JoWkk/view
ANSWERS:
9. (575N)(20.0m)(1) / (10.0s) = 1,150 watts or 1.15kW
10a. (145N)(60.0m)(1) / (25.0s) = 348 watts
10b. twice as fast means half the time, so the power doubles (think about dividing a number by 0.5). 696W
11. (35kg*9.8m/s2)(110m)(1) / (60s) = 630 watts
12. Work = Power * time, so... (65,000W)(35s) = 2,275,000J is the work. Work/displacement = force, so.... 2,275,000J/17.5m) = 130,000N (recall that a J in a Nm)
13. P = W/t, so t = W/P solving.... t = (6,800N)(15m) / (300W) = 340s (when cancelling units, recall that a Watt is a Joule/second)
3. 066B: Power Lab
Chapter 10 pg 274-275: LINK
- overview
- lab write-up document
Put your name/group names at top right, title top center
Section titles:
Hypothesis (make a prediction: Which factors do you think affect power? Then answer the following: What can you do to increase the power you develop as you climb a flight of stairs?)
Materials
Procedure (in your own words)
Data (you need to make a data chart. it must have one row for each person in your group)
Analysis
Conclude & Apply
Going Further
Real-World Physics
- data collection time
HOMEWORK:
1. Try this simple work problem: CH 10: pg 265 #17
#Goals: SWBAT...
1. Write & understand the equations for Total Mechanical Energy
2. Understand the relationship between work and power
3. Solve basic work & power problems
Warm-Up (4min): The Flow of Mechanical Energy
Read, then complete.
Mechanical energy is the energy that is possessed by an object due to its motion or due to its position. Mechanical energy can be either kinetic energy (energy of motion) or potential energy(stored energy of position).
An object that possesses mechanical energy is able to do work
A classic example involves the massive wrecking ball of a demolition machine. The wrecking ball is a massive object that is swung backwards to a high position and allowed to swing forward into building structure or other object in order to demolish it. Upon hitting the structure, the wrecking ball applies a force to it in order to cause the wall of the structure to be displaced. The diagram below depicts the process by which the mechanical energy of a wrecking ball can be used to do work.
Give three more examples of scenarios in which an object uses mechanical energy to do work
CLASSWORK
1. #066A: Total Mechanical Energy Notes
The Total Mechanical Energy
As already mentioned, the mechanical energy of an object can be the result of its motion (i.e., kinetic energy) and/or the result of its stored energy of position (i.e., potential energy). The total amount of mechanical energy is merely the sum of the potential energy and the kinetic energy. This sum is simply referred to as the total mechanical energy (abbreviated TME).
TME = PE + KE
As discussed earlier, there are two forms of potential energy discussed in our course - gravitational potential energy and elastic potential energy. Given this fact, the above equation can be rewritten:
TME = PEgrav + PEspring + KE
The diagram below depicts the motion of Lee Ben Fardest (esteemed American ski jumper) as he glides down the hill and makes one of his record-setting jumps.
Look at the starting and ending energies. Is energy conserved in this example?
The total mechanical energy of Lee Ben Fardest is the sum of the potential and kinetic energies. The two forms of energy sum up to 50 000 Joules. Notice also that the total mechanical energy of Lee Ben Fardest is a constant value throughout his motion. There are conditions under which the total mechanical energy will be a constant value and conditions under which it will be a changing value. This is the subject of Lesson 2 - the work-energy relationship. For now, merely remember that total mechanical energy is the energy possessed by an object due to either its motion or its stored energy of position. The total amount of mechanical energy is merely the sum of these two forms of energy. And finally, an object with mechanical energy is able to do work on another object.
2. #066B: How Does Work...Work?
Let's learn about the relationship between Work & Power: https://ed.ted.com/on/5bau54uF#review
Read questions 1-9
Watch the video and answer the questions/solve the problems
Discuss :-)
At Home Learning (HW)
1. Complete all 9 questions/problems from #066B
If you got stuck, ask a classmate, or contact me via the Remind App
2. #066C: Wednesday we will continue with Power: Watch/take notes/complete edPuzzle on the following:
3. #066D: Weigh yourself. Calculate your mass in kg (2.2lb = 1kg)
4. #066E: Preread the lab (Chapter 10 pg 274-275: LINK).
List the four materials required to do the lab (hint, only three are written, but one big obvious one is in the picture)
WARM-UP
1. What do decibels measure?
2. What's the maximum number of decibels the human ear can handle prior to getting damaged?
CLASSWORK
#066A: HW Review of problem #12 from Day 64 Skill Builder
#066B: Waves Review
This is our mid-unit review. Also, it's a study guide for tomorrow's quiz.
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