Physics Chapter 9 - Energy
134 hp =
100 KW
A 15 kg mass moves with a speed of 12.5 m/s. Calculate the kinetic energy in joules. 2 SF
1200 J
speed is ____
squared
in nuclear reactors, nuclear energy is transformed into
heat
machine
device used to multiply forces or simply change the direction of forces
In what two ways can a machine alter an input force?
direction and magnitude
it takes four times the work to _____ the speed
double
An astronaut in full space gear climbs a vertical ladder on the Earth. Later, the astronaut makes the same climb on the Moon. In which location does the gravitational potential energy of the astronaut change more? Explain.
earth, greater gravity means greater potential energy
the generating plant transforms the energy of falling water into
electrical energy
electrons in motion make
electron currents
for any system in its entirety there is one quantity that doesn't change:
energy
What does it mean to say that in any system the total energy stays the same?
energy is conserved
kinetic energy
energy of motion
potential energy
energy that is stored and held in readiness - because in the stored state it has the potential for doing work
when the nuclei of atoms rearrange themselves,
enormous amounts of energy can be released
friction will require you to exert more _____ without _____
force - greater work input without a greater work output
the work done to stop the car is
friction force x distance of slide
if the box moves at a constant speed you are pushing just hard enough to overcome _____. the net force and net work =
friction, 0
type 1 lever has
fulcrum between the force and the load (or between input and output)
Dry-Rock geothermal power can be a major contributor to power with no pollution. The bottom of a hole drilled down into Earth's interior is fractured, making a large-surfaced hot cavity. Water is introduced from the top by a second hole. Superheated water rising to the surface then drives a conventional turbine to produce electricity. What is the source of energy?
geothermal energy
random molecular motion is sensed as
heat
kinetic energy often appears hidden in different forms of energy such as
heat, sound, light, and electricity
lift two loads up one story of a building, you will be doing twice as much work as if you would have lifted one load, why?
if you move it twice the distance, you'll have to do twice the work
A ramp in a building is an example of which machine?
inclined plane
What simple machine uses a slanted surface that connects a lower level to a higher level?
inclined plane
What type of simple machine is a seesaw on a playground?
inclined plane
Name the four simple machines
inclined plane, lever, wheel and axle, and pulley
What does it mean to say that a machine has a certain mechanical advantage?
it can multiply the force by a certain amount
What would the gravitational potential energy be if the bucket were raised twice as high?
it will double
the advantages of a powerful vehicle is
it's acceleration
Watt equation
joule/sec
energy is measured in
joules
pulley
kind of lever that can be used to change the direction of a force
sliding a load up an incline requires _____ force than lifting it vertically
less
when the load is a wooden crate sliding on a wooden plank, both the actual mechanical advantage and the efficiency will be ______ than if it was an icy plank
less
A fork would be an example of what type of simple machine?
lever
for a type 1 lever, push down on one end and you
lift a load at the other - the directions of input and output are opposite
electrical energy travels through wires to homes where it is used for:
lighting, heating, cooking, and operating electric toothbrushes
an inclined plane is a
machine
In what two ways can a machine alter an input force?(format a,b)
magnitude, direction
The energy due to the position of something or the energy due to motion is called
mechanical energy
PE=
mgh
sound consists of
molecules vibrating in rhythmic patterns
An empty truck traveling at 10 km/h has kinetic energy. How much kinetic energy does it have when it is loaded so its mass is twice, and its speed is increased to twice?
more than four times the KE
we do work when we lift a load against earth's gravity. The heavier the load or the higher we lift it the ________ _______
more work we do
properly used, a bully or system of pulleys can....
multiply forces
if there is some friction, it is the
net force of your push minus the frictional force that is multiplied by the distance
work equation
net force x distance
if there is no change in an object's kinetic energy, then no ____ _____ was done on it
net work
the change in kinetic energy is equal to the
net work done
Is it possible for a machine to multiply energy or work input?
no
carry a load up the stairs - is there a difference if you walk or run?
no - you are doing the same amount of work either way
Mechanical advantage is equal to _________
output force divided by input force
fulcrum
pivot point
a stretched or compressed spring having potential to do work, when a bow is drawn back energy is stored in the bow and the bow can do work on the arrow, a stretched rubber band has potential energy because of its position....these are all types of :
potential energy
the chemical energy in fuels is also
potential energy
the water behind a dam has ______ _____ that is used to power a generating plant below the dam
potential energy
as you draw back the arrow in a bow, you do work stretching the bow. the bow then has ______ ______, when released, the arrow has kinetic energy equal to this _______ ______. It delivers this energy to it's target
potential energy, potential energy
work
product of the force on an object and the distance through which the object is moved
if the speed of an object is doubled, its kinetic energy is ____
quadrupled
the sun shines because some of its nuclear energy is transformed into
radient energy
high powered engines do work
rapidly
for a type 2 lever, you lift the end of the lever. since the input and output forces are on the same side of the fulcrum, the forces have the
same direction
What type of a simple machine would the bottom of a light bulb be?
screw
lever
simple machine made of a bar that turns about a fixed point
kinetic energy depends on
speed squared
energy may change form, but the total energy...
stays the same
it is energy of position at the _______ level
submicroscopic
mechanical enery
the energy due to the position of something or the movement of something
When a driver applies brakes to keep a car going downhill at constant speed and constant kinetic energy, the potential energy of the car decreases. Where does this energy go? Where does most of it go in a hybrid vehicle?
the energy turns to heat - in a hybrid vehicle the energy is turned back into electricity
On what point does a lever pivot?
the fulcrum
type 3 lever has
the fulcrum at one end and the load at the other
for a type 3 lever, the input force is applied between the fulcrum and the load
the input and output forces are on the same side of the fulcrum and have the same direction.
type 2 lever has
the load between the fulcrum and the input force
the kinetic energy of an object depends on....
the mass of the object as well as it's speed
light energy originates in
the motion of electrons within atoms
energy
the property of an object or system that enables it to do work
power definition
the rate at which work is done
mechanical advantage
the ratio of output force to input force for a machine
efficiency of a machine is
the ratio of useful energy output to total energy input - the percentage of the work input that is converted to work output
the work energy theorem states
the relationship between work and energy
if you use a riding lawn mower instead of a push lawn mower, you will have ______ amount of work and _____ amount of power
the same amount of work and more power
A boulder at the top of a vertical cliff has a potential energy of 100 MJ relative to the ground below. It rolls off the cliff. When it is halfway to the ground its kinetic energy is
the same as its potential energy at that point
law of conservation of energy
the study of the forms of energy and the transformations from one form into another
the amount of gravitational potential energy possessed by an elevated object is equal to
the work done against gravity to lift it
Which requires more work, lifting a 10 kg load the vertical distance of 2 m for lifting a 5 kg load a vertical distance of 4 m?
the work is equal
pushing the block of ice 5 times farther up the incline than the vertical distance it's lifted requires a force of only one fifth its weight. if friction is negligible we need to apply only one fifth of the force. the inclined plane shown has a
theoretical mechanical advantage of 5
the high temperature of welding of atomic nuclei is called
thermonuclear fusion
chemical energy
this energy is available when the positions of electric charges within and between molecules are altered and a chemical change takes place
definition of work says nothing about
time or how long it takes to do the work
Distinguish between theoretical mechanical advantage and actual mechanical advantage. How would this compare if the machine were 100% efficient?
tma = no friction, ama with friction
T or F. A compound machine is two or more simple machines that are working together to make work easier.
true
an object moving _______ as fast takes four times as much work to stop
twice
twice as much kinetic energy means
twice as much work
when the rope is pulled 5m with a force of 100 N, a 500 N load is lifted 1 m. what is the mechanical advantage
(500 N)/(100 N) = 5
a child pushes down 10 N and lifts an 80 N load. The mechanical advantage is
(80 N)/(10 N) = 8
(force x distance)input =
(force x distance)output
1 horsepower =
.75 KW
efficiency will always be a fraction less than
1
What is the theoretical mechanical advantage for each of the three lever systems shown?
1, 2, .5
1 KW =
1,000 W
1 MW =
1,000,000 W
Fd=
1/2mv^2
KE=
1/2mv^2
A child on a sled (total weight 500 N) is pulled up a 10-m slope that elevates her a vertical distance of 1 m. What is the theoretical mechanical advantage of the slope?
10
Clyde, a stubborn 3500 N mule, refuses to walk into the barn, so Farmer McDonald must drag him up a 5.0 m ramp to his stall, which stands 0.50 m above ground level. What is the ideal mechanical advantage of the ramp?
10
How many joules of work are done on an object when a force of 10 N pushes it a distance of 10 m?
100 J
If you do 100J of work to elevate a bucket of water, what is its gravitational potential energy relative to its starting position?
100 J
you lift a 100-N boulder 1 m - how much work is done on the boulder, what power is expended if you lift the boulder in a time of 2 s, and what is the gravitational potential energy of the boulder in the lifted position?
100 J, 50 W, 100J
an icy plank used to slide a block of ice up to some height might have an efficiency of almost
100%
A bullet of mass 50 g strikes a wooden block of mass 5 kg. The bullet becomes embedded in the block. The block with a bullet in it then flies off at 10 m/s. What was the original velocity of the bullet? 1SF
1000 m/s
Calculate the work done lifting a 500 N barbell 2.2 m above the floor. (2SF)
1100 J
A loaded sled weighing 800 N is pulled a distance of 200 m. To do this, a force of 120 N is exerted on a rope which makes an angle of 60° with the horizontal. How much work is done?(2SF)
12000 J
The package weighs 35 N. A person carries the package from the ground floor to the fifth floor the office building, or 15 m upward. The person weighs 750 N. How much total work is done?
12000 J
A 1600 kg car travels at a speed of 12.5 m/s. What is its kinetic energy?(use joules)
130000 J
A crate of bananas weighing 3000. N is shipped from South America to New York, where it is unloaded by a dock worker who lifts the crate by pulling with a force of 200. N on the rope of a pulley system. What is the actual mechanical advantage of the pulley system?
15.0
Auto companies frequently test the safety of automobiles by putting them through crash test to observe the integrity of the passenger compartment. If a 1000. kg car you sent toward a cement wall with a speed of 14 m/s and the impact brings it to a stop in 0.08 s, with what average force is it brought to rest? 2 SF
180000 N
A 200 kg hammer of a pile driver is lifted 10 m. Find the potential energy of the system where the hammer is at this height. Use 3 SF.
19,600 J
Calculate the work done when a force of 1 N moves a book 2 m
2 J
Calculate the number of joules of kinetic energy a one kilogram book has when tossed across the room at a speed of 2m/s
2 joules
Rhonda, who has a mass of 60.0kg, is riding at 25.0 m/s in her sports car when she must suddenly slam on the brakes to avoid hitting a dog crossing the road. She is wearing her seatbelt, which brings her body to a stop in 0.400 seconds.If she had not been wearing her seatbelt, and the windshield has stopped her head in .001 s, what the average force with the windshield had exerted on her?
2,000,000 N
How much power is required to do 100 tools of work on an object in a time of 0.5 seconds? How much power is required if the same work is done in one second? ( use form XXX W, XXX W)
200 W, 100 W
Find the potential energy of a 10 kg mass when it is raised to a height of 20 m. Use 1 SF
2000 J
A box that weighs 1000 N is lifted a distance of 20 m straight up by a rope and pulley system. The work is done in 10 seconds. What amount of power is used in Watts?
2000 W
Suppose that you apply a 60-N horizontal force to a 32-kg package, which pushes it 4 meters across a mailroom floor. How much work do you do on the package?
240 J
A 60 kg shell is shot from a cannon to a height of 400 m. What is the potential energy of the earth-shell system when the shell is at this height? Use 2 SF
240,000 J
Katie, a 30. kg child, climbs a tree to rescue her cat who is afraid to jump 8.0 m to the ground. How much work does Katie do in order to reach the cat?
2400 J
After finishing her physics homework, Sherri pulls her 50.0 kg body out of the living room chair and climbs up the 5.0 m high flight of stairs to her bedroom. How much works does Sherri do in ascending the stairs?
2500 J
A greyhound at a race track can run at a speed of 16.0 m/s. What is the KE energy of a 20.0 kg greyhound as it crosses the finish line?
2560 J
Calculate the work needed to lift a 90N block of ice a vertical distance of 3 m. What potential energy does it have?
270 J, 270 J
A person who weighs 630 N climbs 5 m of a ladder. What is the increase in the potential energy of the earth-person system when the person is at this height? Use 1 SF
3,000 J
A motor operates an endless conveyor belt. The motor produces a force of 500. N on the belt and moves it at the rate of 6.5 m/s. What is the power of the motor in kilowatts?
3.3 kW
If 270 million people in United States all jumped up in the air simultaneously pushing off earth with an average force of 800. N each for a time of 0.10 seconds, what velocity would the 5.98×10^24 kg Earth move?
3.6X10^-15m/s
A 50 kg student runs up a flight of stairs that is 6 m high. How much work is done?
3000 J
A person who weighs 630 N climbs 5 m of a ladder. What work does the person do? Use 1 SF
3000 J
A force of 800 N is needed to push a car across a lot. Two students push the car 40 m. How much work is done?(2SF)
32000 J
What is the efficiency of a machine that requires 100 J of energy to do 35 J of work?
35%
Rhonda, who has a mass of 60.0kg, is riding at 25.0 m/s in her sports car when she must suddenly slam on the brakes to avoid hitting a dog crossing the road. She is wearing her seatbelt, which brings her body to a stop in 0.400 seconds. What is the average force the seat belt exerted on her?
3750 N
How many joules of potential energy does a one kilogram book gain when is elevated 4 m? Use 2 SF
39 J
What is the mechanical advantage if 50 J are put in and 200 J are produced?
4
a hammer falls off a rooftop and strikes the ground with a certain kinetic energy. If it fell from a roof that was four times higher, how would its kinetic energy of impact compare? It's speed of impact? (neglect air resistance.)
4 times greater, 16 times greater
a car moving at twice the speed of another has _____ times as much kinetic energy, and will require _____ times as much work to stop
4, 4
Calculate the change in potential energy of 8,000,000 kg of water dropping 50 m over Niagara Falls.
4,000,000,000 J
Calculate the increase in potential energy when a 20 kg block of ice is listed a vertical distance of 2 m
400 J
In electric motor lifts a 2000 kg elevator 18 m in 40 seconds. How much work is done?
400000 J
A diesel engine lives the 225 kg hammer of a piledriver 20.0 m in five seconds. How much work is done on the hammer?
44100 J
What work is done to lift a 49 kg crate a distance of 10 m. (2SF)
4800 J
Relative to the ground below, how many Joules of potential energy does a 1000 N boulder have at the top of a 5 m ledge?
49,000 J
Jeanie rolls a 7 kg bowling ball down the alley for the league championship. One pin is still standing, and Jeanie hits it head on with a velocity of 9.0 m/s. The 2.0 kg pin acquires a forward velocity of 14.0 m/s. What is the new velocity of the bowling ball?
5 m/s
What will be the kinetic energy of an arrow having a potential energy of 50 J after it is shot from a bow?
50 J
A coolie carries a load of 500 N to a distance of 100 m. The work done by him is
50,000 N-m
if the circular distance the handle is moved is 500 times greater than the distance between ridges, then the theoretical mechanical advantage of the jack is ______. there is a great deal of friction in the jack, so the efficiency might be about ____20%. this means that the jack actually multiplies the force by about _____ times so the mechanical advantage is about ____%
500, 20%, 100, 100%
How much work is required to increased the kinetic energy of a car by 5000 J?
5000 J
The package weighs 35 N. A person carries the package from the ground floor to the fifth floor the office building, or 15 m upward. How much work does the person do on the package?
530 J
Calculate the power expended when a 500. N barbell is lifted 2.2 m in 2.0 seconds
550 W
How much work is done to lift a 60 kg crate a vertical distance of 10 m? (3SF)
5880 J
It is said that Galileo dropped objects off The Leaning Tower of Pisa to determine whether heavy or light objects fall faster. If Galileo had dropped a 5.0 kg cannon ball to the ground from a height of 12 m, what would have been the change in potential energy of the cannonball?
590 J
if we do 100 J of work, the friction on the pulley as they turn and rub on their axle can dissipate 40 J of heat energy. this pulley system has an efficiency of __%
60%
A 16 kg stone falls 40.0 m. Find the stones kinetic energy in joules, just before it strikes the ground
6300 J
A block that weighs 98 N drops 64 m. What does the kinetic energy of the block just as it strikes the ground?(use Joules)
6300 J
A force of 600 N is applied to a metal box to pull in across a floor. The rope used to pull the boxes held at an angle of 46° with the floor. The boxes moved to a distance of 15 m. How much work is done? (2SF)
6300 J
Bud, a very large man of mass 130 kg, stands on a pogo stick. How much work is done as Bud compresses the spring of the pogo stick 0.50 m?
640 J
A car has a mass of 1500 kg. What is its kinetic energy if it has a speed of 30 m/s?(use Joules and 2 SF)
680000 J
Clyde, a stubborn 3500 N mule, refuses to walk into the barn, so Farmer McDonald must drag him up a 5.0 m ramp to his stall, which stands 0.50 m above ground level. If Farmer McDonald needs to exert a 450 Newton force on the mule to drag him up the ramp with a constant speed, what is the actual mechanical advantage of the ramp?
7.8
Calculate the work done when a 20 Newton force pushes a car 3.5 m
70 J
The 2000 Belmont stakes winner, Commendable, ran the horse race at an average speed of 15.98 m/s. If Commendable and jockey Pat Day had a combined mass of 550.0 kg, what was their kinetic energy as they cross the finish line?
70220 J
How many joules of potential energy does a one kilogram book gain when is elevated 8 m? Use 2 SF
78 J
If a car traveling at 60 km/hr will skid 20 m when it brakes lock, how far will it skid if it is traveling at 120 km/h when its brakes lock?
80 m
After finishing her physics homework, Sherri pulls her 50.0 kg body out of the living room chair and climbs up the 5.0 m high flight of stairs to her bedroom. If Sherry runs up the stairs in three seconds, how much power did Sherry generate?
820 W
A diesel engine lives the 225 kg hammer of a piledriver 20.0 m in five seconds. What is the power of the engine in Watts?
8820 W
Jamall is at the state fair playing some of the games. At one booth he throws a 0.50Kg ball with a velocity of 21.0 m/s in order to hit a 0.20 Kg bottle sitting on a shelf. When he makes contact the bottle goes flying forward at 30.0 m/s. What is the velocity of the ball after it hits the bottle?
9 m/s
When the brakes of a car are locked, the car skids to a stop. How much farther will the car skid if it's moving 3 times as fast?
9 times farther
In electric motor lifts a 2000 kg elevator 18 m in 40 seconds. What is the power of the motor in Watts?
9000 W
An 8 kg mass drops 12 m. In joules what is the kinetic energy of the mass just before it strikes the ground? use 2 SF
940 J
if we put in 100 J of work on a lever and get out 98 J of work, the lever is __% efficient. we lose _ J of work input as heat
98%, 2
A friend says that if you do 100 J of work on a moving cart, the cart will gain 100 J of KE. Another friend says this depends on whether or not there is friction. What is your opinion of these statements?
I agree because friction will take away KE
If a forklift is replaced with a new forklift that has twice the power, how much greater a load can it lift in the same amount of time? If it lifts the same load, how much faster can it operate?
It should be able to lift twice as much in the same amount of time. It can lift it twice as fast if it has twice the power.
Which requires more work: stretching a strong spring a certain distance or stretching a weak spring the same distance? Defend your answer
More force is required to stretch the strong spring, so more work is done in stretching it the same distance as a weaker spring.
Joule unit
N-m
work unit
N-m
Does using an automobile's air conditioner while driving increase fuel consumption? What about driving with the lights on? What about playing the car radio when part with the engine off? Explain in terms of conservation of energy.
Running the air conditioner uses gas because the energy to run the air conditioner comes from the engine and the engine's energy comes from the gasoline. Light's use energy and the energy comes from the engine and the engine gets energy from fuel. The radio uses gas because it gets its energy from the engine which gets it's energy from gas
T or F. The purpose of a simple machine to make work easier by allowing for a push or pull to occur over an increased distance
True
A force sets an object in motion. When the force is multiplied by the time of its application, we called the quantity impulse, which changes the momentum of that object. What do we call the quantity force times distance, and what quantity can this change?
We call force x distance work, and it can change the energy of an object
The energy really required to live comes from the chemically stored potential energy in food, which is transformed into other energy forms during the digestion process. What happens to a person whose combined work and heat output is less than the energy consumed? What happens when the person's work and heat output is greater in the energy consumed? Can an undernourished person perform extra work without extra food?
Weight (mass) is gained, weight is not lost, not without losing more weight
What way is a machine subject to the law of energy conservation? Is it possible for a machine to multiply energy or work input?
Work out cannot exceed work put in. It is not possible.
each atom that makes up matter is
a concentrated bundle of energy
efficiency = (ratio)
actual mechanical advantage / theoretical mechanical advantage
what 2 factors affect work
application of force, movement of something (by that force)
Atlas and Hercules, two Carnival slideshow strongman, each lift 200. kg barbells 2.00 m off the ground. Atlas lifts his barbells in 1.00s and Hercules lifts his barbells in 3.00s. Which strongman is more powerful?
atlas
Atlas and Hercules, two Carnival slideshow strongman, each lift 200. kg barbells 2.00 m off the ground. Atlas lifts his barbells in 1.00s and Hercules lifts his barbells in 3.00s. Which strongman does more work?
both did the same amount of work
work equals
change in kinetic energy
In what sense is energy from coal actually solar energy?
coal is formed from organic material. organic materials get their energy from the sun
Which type of lever is the output force smaller than the input force?
type 3 lever
efficiency =
useful work output / total work input
gravitational potential energy =
weight x height
if an object is moving, ______ is required to bring it to rest
work
to increase the kinetic energy of an object, ______ must be done on the object
work
net work
work based on the net force
power equation
work done / time interval
gravitational potential energy
work is required to elevate objects against earth's gravity - the potential energy due to elevated positions
the more kinetic energy something has, the more
work is required to stop it
work input =
work output
push against a box on a floor: if it doesn't slide then you are not doing ______, on a very slippery floor, if there is no friction at all , the work of your push times the distance of your push appears as _____ ___ of the box
work, kinetic energy
work =
∆KE
