Download Week 10-11 Work power and Energy

Mr. Wolf
Physics 1
Name: ____________________
Date: ______
Work, Power and Energy
This packet will cover all of the material for chapters 3.2 and 4.1. YOU will be responsible for
having this in class every day. Included in this packet are the note sheets, homework, and lab
activities.
IF YOU MISS A CLASS PERIOD IT IS YOUR RESPONSIBILITY TO DETERMINE THE
WORK ASSIGNED. Check the website, email MR. WOLF or a classmate.
Website:
Mr. Wolf’s email:
mrwolfteacher.com
[email protected]
Assignment
Work and Power HW
Page #
4
RaTN – Types of Energy
7-10
Work power and Energy Review
15-16
RaTN Conservation of Energy
17-18
Work
Power
Joule
Watt
Kinetic Energy
Gravitational Potential Energy
Date due:
Important Vocabulary
Conservation of Energy
Horsepower
Calorie
work
Power 

time
W  Fd
1
KE  mv 2
2
PE  mgh


DO NOT LOSE THIS PACKET.
You will lose points if your have to get a new one.
This packet will be collected at the start of the weekly quiz on Friday _______.
Notes – Work and Power
Warm Up
A. Give 3 different examples of something that has energy.
B. If the toaster crashes into your Windows, how do we know that there was a force applied
on the toaster by Windows? (Think about Newton’s Laws.)
Questions
1. Define Energy –
2. Define Work –
3. What does work depend on? Write the equation, and the units
4. How much work does a person do while pushing a chair with a force of 5 N for 3 meters?
Givens:
Want:
Formula:
Solve:
5. How much work do you do lifting a stack of books three meters if the books weigh 20N?
Givens:
Want:
Formula:
6. What does it mean to do work against gravity?
Solve:
7. Define Power –
8. Write the equation for power, and the units.
9. Find a heavy object (a backpack is sufficient) that you can lift and weigh it.
Weight of the object: _____________ Newtons
10. Locate an open space in the classroom where you can lift the object, without hitting
anything. Using a meter stick, measure the height you will be lifting the object.
Distance: _____ meters
11. Calculate the work done lifting the object. What are the units?
Givens:
Want:
Formula:
Solve:
12. Lift the object to the same height again while two students measure the time, each with
their own stopwatches. Average the times this will help eliminate error.
Time 1: _________
Time 2: _________
Average time: _________
13. Calculate your power while lifting the object. What are the units? (See equation above and
SHOW YOUR WORK)
Givens:
Want:
Formula:
Solve:
Work and Power HW Problems
1. You pick up a 10-newton book off the floor and put it on a shelf 2 meters high. How much
work did you do?
Givens:
Want:
Formula:
Solve:
2. Alejandra weighs 225 newtons. How much work does she do against gravity when she
climbs to a ledge at the top of a 15-meter climbing wall?
Givens:
Want:
Formula:
Solve:
3. Jai-Anna, who has a mass of 45 kilograms, climbed 3 meters up a ladder to rescue her cat
from a tree. How much work against gravity did she do?
Givens:
Want:
Formula:
Solve:
4. Elijah does 44 joules of work against gravity to pull a 0.5-kilogram rope with a 1.0-kilogram
bucket attached up to the floor of his tree house. How many meters high is his tree house?
Givens:
Want:
Formula:
Solve:
5. A motor does 5,000 joules of work in 20 seconds. What is the power of the motor?
Givens:
Want:
Formula:
Solve:
6. A hair dryer uses 72,000 joules of energy in 1 minute. What is the power of this hair dryer?
Givens:
Want:
Formula:
Solve:
7. Emily’s vacuum cleaner has a power rating of 200 watts. If the vacuum cleaner does
360,000 joules of work, how long did Emily spend vacuuming?
Givens:
Want:
Formula:
Solve:
8. A 1000-watt microwave oven takes 90 seconds to heat a bowl of soup. How many joules of
energy does it use?
Givens:
Want:
Formula:
Solve:
Watts your horsepower?
Purpose:
To investigate the work done and power output of a person climbing stairs
Procedure:
Work  force  distance

Power 
work
time
1 Watt 1
Joule
second
For this lab you will measure the work and power necessary to run up a set of stairs.
 be climbing the stairs using the
1) First you must determine the weight of the person who will
force plate. (This does not change throughout the lab.)
Weight (Newtons): _________
2) Now find a section of stairs where you will have space to move up and down them freely.
Using the meter stick find the height of one stair and multiply this by the number of stairs
you climb. This will give you the total height you climb.
3) Now walk/jog/run up the stairs while your partner measures your time. Record it in the
appropriate table below. AFTER BOTH people have run, complete the table calculating
the work and power.
Walking
Single stair
height (m)
Number
of stairs
Total height
of all stairs
Weight (N)
Work (J)
Time (s)
Power (W)
Jogging
Single stair
height (m)
Number
of stairs
Total height
of all stairs
Weight (N)
Work (J)
Time (s)
Power (W)
Running
Single stair
height (m)
Number
of stairs
Total height
of all stairs
Weight (N)
Work (J)
Time (s)
Power (W)
Part 2: Analysis
After collecting your data answer the following questions using complete sentences and
showing your work.
1) Power is the ___________ at which work is done, or how much energy is transferred every
second. The formula for power is ___________ divided by ___________. If you do work
fast you have a greater ___________.
2) Why was the work done for all three trials the same even though the speeds were
different? Think about the variables in the formula when you answer.
3) Was the power different for each trial, if so why? Think about which quantities power
depends on, and what changed during the different trials.
4) Convert the power you used walking/jogging/running up the stairs into horsepower. Show
your work.
1 horsepower (hp) = 746 W
Walking
Horsepower
(hp)
Jogging
Running
RaTN – Types of Energy
Energy and the Conservation of Energy
What is Energy?
What do we mean when we say “the system” in physics? (use the
definition from the back of the book)
What is the definition of energy?
A definition
of energy
What types of changes can energy cause? There are a bunch of things,
so don’t just write one.
Write down at least three examples of ways that energy is used to create
change in a real-world system.
Examples
What are the units that we will use for energy? (name and abbreviation)
Units of
energy
What is one joule?
What is work?
What are some different meanings of work?

“Work”
means
different
things



Definition of work:
What “work
means in
physics
How far must you lift a block with a weight of 1 Newton to do 1 joule of work?
___________ is done on ___________. If you life a _____________ one
___________ with a ____________ of one _______________, you have
done one _____________ of ______________ on the _______________.
Work is done
on objects
Force 
Work


=


Distance


in the direction of the force
In order to do work what must an object have?
Energy is
needed to do
work


What is another way to think about energy?
Potential Energy
What does the word potential mean?
What is
potential
energy?
_______________ or _______________ with _________________
______________ are able to exert __________________
(________________ _____________) as they change to other
arrangements.
Gravitational
Energy
Mr. Wolf lifts a 12 kg block of homework papers above his head. When does
it have more gravitational potential energy? Before he lifts it or after he lifts it?
Why? (Look at the picture to the right. It might help you answer this
question.)
The block’s _________________ ______________ is exactly the amount of
__________ it can do as it goes __________.
Multiplying the ___________ by the ____________ gives you the block’s
How to
calculate
potential
energy
_________________ ____________ at any given _______________.
Mass ____ 
Potential Energy


PE =
accelerati on due to gravity


Height


Kinetic Energy
Objects that are ___________ have the ability to ___________ __________.
Kinetic
Energy is the
energy of
motion
_____________ of _______________ is called ___________ ___________.
Kinetic energy can be easily converted into what other type of energy?
The amount of ____________ ___________ an object has __________ the
Kinetic
Energy can
do work
Kinetic
energy
depends on
mass and
speed
amount of ___________ the object can do by ____________ a ___________
as it stops.
You need to write your own notes here. Write down why kinetic energy
depends on mass and velocity in your own words.
The _____________ _______________ of a _____________ object is
________ to ________ _________ its ___________ _____________ by the
Formula for
kinetic
energy
square of its __________.
Mass ____ 
Kinetic Energy


KE =
Velocity
What happens to the kinetic energy if the velocity doubles?
Kinetic
energy
What about if it triples?
increases as
the square of
the speed
What happens to the kinetic energy if the velocity is cut in HALF?
(next page)
List any questions that you may have.


Energy Notes: KE & PE
Warm Up
A. List some of the ways in which the word “work” is used in everyday language.
B. List some of the ways in which the word energy is used in everyday language.
C. Where do you get your energy to live? Where does THAT energy come from?
D. Suppose a force of 100 newtons is used to push an object a distance of 5 meters in 15
seconds. Find the work done and the power for this situation.
Questions
1. Define – Kinetic Energy:
2.
What is the operational definition for KE?
3. What is the kinetic energy of a 3-kg ball traveling 4 m/s?
Givens:
Want:
Formula:
Solve:
4. What is the kinetic energy of a 3-kg object traveling 8 m/s?
Givens:
Want:
Formula:
Solve:
5. A car has a KE of 1000J.
a. If the car’s velocity doubles, what is the new kinetic energy?
b. If the car’s velocity is cut in half, what is the new kinetic energy?
6. Define – Potential Energy:
7. What are some of the types of potential energy?
8. How do we calculate gravitational potential energy? What are the units?
9. You slide a 1 kg book across a level table. How much potential energy is gained?
10. You lift the same 1 kg book 1.5m above your head. How much potential energy is gained?
Givens:
Want:
Formula:
Solve:
11. You drop that 1 kg book and it falls to the ground (1.5 m). How much potential energy is
lost?
12. How is work related to:
a. Gravitational Potential Energy?
b. Kinetic Energy?
13. How do we show energy is gained? How do we show that energy is lost?
FROGGY!
Lightly press down your frog-on-a-spring. It will jump up like a real frog. And also like a real
frog, it will never jump if you press down on it too hard. You will be using your frog to study
potential and kinetic energy.
PART 1: JUMP, FROGGY, JUMP!
1) Hold a meter stick next to your frog. Let him jump and measure how far he travels. Repeat
for a total of 5 trials. Find the average.
(Remember to convert from cm to m)
Trial
1
2
3
4
5
Average
Jump height (cm)
Jump height (m)
2) Using the average jump height in METERS, calculate the gravitational potential energy of
your frog at the top of his path. You’ll get a tiny amount!
Info you’ll need: the mass of your froggy is 0.005 kg.
Givens:
Want:
Formula:
Solve:
3) What is the froggy’s velocity at the top of its path? (Think about free fall) ________
4) Therefore does the frog have any kinetic energy at the top of its path? ______
5) Use the potential energy at the top of its flight and your answer to #4 to determine the total
energy of the frog system.
6) When the frog falls back down, what is the kinetic energy the INSTANT BEFORE it strikes
the table? Think about the conservation of energy and what the potential energy is right
before the frog lands. (Don’t answer zero – I want the KE when he is just starting to land.)
7) When the frog jumped off of the table, what was his kinetic energy? This is a question that
requires thinking, not calculating.
8) Use your answer from #7 to calculate the frog’s velocity when he jumped off of the table.
Using the formula for kinetic energy we can rearrange it to solve for the velocity.
1
KE  mv 2
2
Givens:
Rearranged,
v
2  KE
m
Now plug in the numerical values of KE and m and calculate v.
Want:
Formula:
Solve:


PART 2: THINK ABOUT YOUR FROGGY
1) When you push your froggy down with some force for some distance, you are doing
_________. Remember, force x distance = __________. If you push the froggy’s spring
down more quickly, you have greater ____________.
2) When you do work to the frog, you are causing it to store energy in the spring. Stored
energy is called _____________ energy. We have been talking about gravitational
____________ ____________ during this chapter, but the potential energy in the frog’s
spring is called elastic potential energy.
3) The law of ______________ of energy tells us that the total amount of energy an object
has never changes unless some outside ____________ acts on it (like friction or the force
when it smashes into another object).
4) When you push the frog down, you give it some amount of potential _________. When it
jumps up, it uses its potential energy to move. As soon as its spring is extended and it
starts to leave the table, it is moving at some velocity and therefore has ____________
energy. After an object is launched up into the air, its velocity decreases due to gravity, so
its ___________ energy decreases.
5) As the frog moves up, its gravitational _____________ energy increases. The formula for
gravitational potential energy is _____________.
6) At the top of its path, the frog has a velocity of __________ and therefore, has a
____________ energy of zero. It only has gravitational ___________ energy at the top. As
it falls back down toward the table, its ____________ energy increases.
Work Power and Energy Review
1. If a small machine does 2,500 joules of work on an object to move it a distance of 100
meters in 10 seconds;
a. What is the force needed to do the work?
Givens:
Want:
Formula:
Solve:
b. What is the power of the machine doing the work?
Givens:
Want:
Formula:
Solve:
2. A force of 100 newtons is used to move an object a distance of 15 meters with a power of
25 watts. Find the work done and the time it takes to do the work.
Givens:
Want:
Formula:
Solve:
Givens:
Want:
Formula:
Solve:
3. A machine that uses 200 watts of power moves an object a distance of 15 meters in 25
seconds. Find the force needed and the work done by this machine.
Givens:
Want:
Formula:
Solve:
Givens:
Want:
Formula:
Solve:
4. The potential energy of an apple is 6.00 joules. The apple is 3.00-meters high. What is the
mass of the apple?
Givens:
Want:
Formula:
Solve:
5. Two objects were lifted by a machine. One object had a mass of 2 kilograms, and was lifted
at a speed of 2 m/sec. The other had a mass of 4 kilograms and was lifted at a rate of 3
m/sec.
a. Which object had more kinetic energy while it was being lifted?
b. Which object had more potential energy when it was lifted to a distance of 10
meters? Show your calculation. (Remember that gravity = 9.8 m/sec2)
Givens:
Want:
Formula:
Solve:
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9. What is the potential energy of a 3 kilogram-ball that is on the ground?
Givens:
Want:
Formula:
Solve:
10. What is the kinetic energy of a 2,000-kilogram boat moving at 5 m/sec?
Givens:
Want:
Formula:
Solve:
11. Define the following terms:
a. Work –
b. Power –
c. Kinetic Energy –
d. Potential Energy –
12. An object has 50 Joules of kinetic energy. What is the energy if you…
a. Double the speed?
b. Cut the speed in half?
c. Double the mass?
d. Reduce the mass by half?
13. Trace the energy flow from the sun to you, what gives you energy to climb the stairs?
14. List 3 different forms of energy?
15. What are other forms of potential energy?
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RaTN – Conservation of Energy
Answer the following questions or provide your own explanations based on reading pages 7072 in the textbook.
1. What happens to the kinetic energy of ball as it is thrown up in the air?
2. What does the saying ‘Energy is conserved’ mean? (Don’t just write down the blue words,
what are the other important ideas here?)
3. How can the exact launch speed of a ball help you? What can you determine if you know
the exact launch speed based on the conservation of energy?
4. You throw a ball up in the air. What do you know about the kinetic energy and speed when
it lands back in your hand?
5. By turning on a light bulb what are you doing in a physics sense? What forms are you
converting the energy from and to?
6. How can you say that power plants don’t make energy? What do they do?
Continue on to the next page…
17
Read pages 240 to 241, while taking notes in the boxes below on important information for the
section
10.1 Energy Flow
Energy and systems
Energy as nature’s
“money”
An example
Possible or
impossible?
Energy exists in many different forms
Mechanical energy
Radiant energy
Electrical energy
Chemical energy
Nuclear energy
Thermal energy
Pressure
18
Roller Coaster Physics
The energy of the rollercoaster car is conserved. Calculate the potential energy, kinetic
energy, and speed of the frictionless rollercoaster at each point below. The roller coaster
starts from rest at point A.
A: h = 45m
PE  mgh KE  1 mv2
2
D: h = 38m
m=
1000kg
B: h = 30m
E: h = 20m
C: h = 20m
F: h = 0m
1. Calculate the potential energy at each point.
Mass
Acceleration due
Point
(kg)
to gravity (m/s2)
A
Height
(m)
Gravitational Potential
Energy (J)
B
C
D
E
F
2. At what point is the gravitational potential energy the greatest? _______
3. At what point is the gravitational potential energy the least? _______
4. What happens to the gravitational potential energy as the roller coaster goes down the
track? Where does it go?
19
5. Complete the table below, solving for the kinetic energy of the roller coaster.
Gravitational
Point
Kinetic Energy (J)
Total Energy (J)
Potential Energy (J)
A
0
B
C
D
E
F
6. At what point is the kinetic energy the least? ______
7. At what point is the kinetic energy the greatest? ______
8. When is the roller coaster’s velocity the greatest? ______
9. Points C and E are at the same height. How does the kinetic energy of the roller coaster
car compare at these points?
a. Compare the velocities at these two points?
10. Did the total energy of the roller coaster car ever change? Explain.
What does it mean to say that energy is conserved? Write a definition for the Law of
Conservation of Energy in
20
NOVA Car Crash Video Worksheet
Answer the following questions as you watch the video.
1. Why did it take so long for automobile makers to begin safety testing their products? (there
are several reasons and they aren’t all listed at the same time)
2. When and where was the first car manufactured?
3. What was the first part of cars to be made safer? (explain how it works)
4. What is the glass necklace and why is it such a big deal? How was it remedied?
5. Who was Hugh deHavens, and what did he contribute to the automobile safety industry?
(Many things, so be concise)
6. What has been the single most effective safety device in any vehicle?
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7. What was the very important invention that Bela Berenyi came up with? How does it help
to save people’s lives?
8. How expensive are anthropometric dummies? (They are more expensive now!)
9. Why do we use dummies? (Again, there are several reasons)
10. What does Ralph Nader have to do with car safety?
11. Explain why it took so long for an effective airbag to be manufactured.
12. What is the “darker side” of airbags?
13. What do you think of the automated highways? Explain why you would either be for or
against them.
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