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Preparation for Physics Final > Chapter 9 > Flashcards

Chapter 9 Flashcards

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1
Q

What is work?

A

The product of the net force on an object
and the distance through which the object is moved.

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2
Q

Do we do work when we lift a load against Earth’s gravity?

A

Yes

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3
Q

The _______the load or the ________we lift it, the more _______we do.

A

heavier; higher; work

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4
Q

______ is done when a ______ acts on an _______ and the object moves in the _______ of the force.

A

Work; force; object; direction

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5
Q

What is the equation of Work?

A

W=Fd

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6
Q

If we lift two loads up one story, we do _____ as much _____as we would in lifting one load the same distance

A

twice; work

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7
Q

If we lift one load two stories instead of one story, we do _____ as much work because the ______ is twice as great

A

twice; distance

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8
Q

Is work done if the object is not moved by the exerted force and in the direction of the force?

A

No

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9
Q

If a weighlifter is holding the barbell in the air, there is not work on the barbell. Where is work done?

A

On the muscles by stretching and squeezing them

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10
Q

How many categories does work fall into to?

A

two

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11
Q

11). What is one of the categories work falls into?

A

Work done against another force

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12
Q

Example of #11

A

When an archer stretches her bowstring, she is doing work against the elastic forces of the bow. Push-ups (against the force of your own weight)

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13
Q

You do _____ on something when you force it to move _______ the influence of an _______ force—often friction.

A

work; against; opposing

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14
Q

14). The other category of work is work done to…

A

change the speed of an object

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15
Q

Example of #14

A

bringing an automobile up to speed or in slowing it down.

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16
Q

In both categories, work involves __________between something and its surroundings.

A

a transfer of energy

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17
Q

What is the unit of work?

A

Joule (J)

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18
Q

Does the definition of work say something about how long it takes to do the work?

A

No

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19
Q

When carrying a load up some stairs, do you do the same amount of work whether you walk or run up the stairs?

A

Yes

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20
Q

What does power equal?

A

Power equals the amount of work done divided by the time interval during which the work is done.

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21
Q

Does a high powered engine do work rapidly?

A

Yes

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22
Q

Does an automobile engine that delievers twice the power of another automobile produce twice as much work or go twice as fast as the less powerful engine?

A

No

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23
Q

Twice the power means…

A

It can do twice as much work in the same amount of time or the same amount of work in half the time

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24
Q

What is the unit of power

A

J/s or watts (W)

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25
Why was Watt named Watt?
In honor of James Watt, the 18th century developer of the steam engine
26
One kilowatt equals...
1000W
27
In the U.S., we rate engines in units of..
Horsepower and electricity kilowatts
28
One horsepower(hp) is the same as...
0.75kW
29
When work is done by an archer in drawing back a bowstring, the bent bow acquires...
the ability to do work on the arrow
30
In what situations may an object acquire the ability to do work?
ompression of atoms in the material of an object; a physical separation of attracting bodies; or a rearrangement of electric charges in the molecules of a substance.
31
Energy
The property of an object or system that enables it to do work
32
What is energy measured in?
Joules
33
Mechanical energy
the energy due to the position of something or the movement of something
34
What are two forms of mechanical energy
Kinetic and Potential Energy
35
Potential Energy
Energy that is stored and held in readiness
36
What are three examples of potential energy?
elastic potential energy, chemical energy, and gravitational potential energy
37
What type of energy does a stretched or compressed spring have?
Elastic Potential Energy
38
What is elastic potential energy?
When an object has the ability to do work bc of its position.
39
Are the chemical energy in fuels also potential energy?
Yes
40
What is chemical energy?
energy of position at the submicroscopic level
41
When is chemical energy available?
when the positions of electric charges within and between molecules are altered, that is, when a chemical change takes place.
42
Gravitational Potential energy
The potential energy due to elevated positions
43
What is the amount of gravitational potential energy possessed by an elevated object is equal to...
the work done against gravity in lifting it
44
Gravitational potential energy's formula is...
mgh
45
The gravitational potential energy is relative to that ________and depends only on mg and h
level
46
If you’re in a third-story classroom and a ball rests on the floor, you can say the ball is at height ___. Lift it and it has ________ PE relative to the floor. Toss it out the window and it has __________ PE relative to the floor
0; positive; negative
47
How do hydroelectric power stations make use of gravitational potential energy?
Water from an upper reservoir flows through a long tunnel to an electric generator.
48
Gravitational potential energy of water is converted into...
electrical energy
49
If an object is moving, is it capable of doing work?
Yes
50
What is kinetic energy
Energy of motion
51
The ____________ of a moving object is ______ to the work required to bring it to its speed from rest, or the work the object can do while being brought to rest
Kinetic Energy; equal
52
If the speed is squared (doibled) the kinetic energy is...
quadrupled and takes 4x as much work to stop
53
What does the work energy theorem state?
whenever work is done, energy changes
54
Work =...
change in kinetic energy
55
What does the work-energy theorem emphasizes?
the role of change
56
If there is no change in a object's KE, the no ______was done on it.
net work
57
The net force minus the frictional force times the distance equals...
KE
58
Is the force of friction an independent variable?
Yes
59
How does kinetic energy appear?
heat, sound, light, and electricity
60
What does the law if conservation of energy state?
Energy cannot be created or destroyed. It can be transformed from one form into another, but the total amount of energy never changes.
61
Energy may change form, but...
the total energy score stays the same
62
Each atom that makes up matter is a...
concentrated bundle of energy
63
Enormous compression due to gravity in the deep hot interior of the sun causes hydrogen nuclei to...
fuse and become helium nuclei
64
What dies thermonuclear fusion due?
It releases radiant energy
65
Machine
A device used to multiply forces or simply to change the direction of forces.
66
A machine ________ energy from one place to another or _________ it from one form to another
transfers; transforms
67
Lever
a simple machine made of a bar that turns about a fixed point
68
The work input of a lever equals the....
work out (if the friction is small enough to neglect)
69
The fd(in) of the lever equals the...
fd(out)
70
What is the fulcrum?
The pivot point
71
The ratio of output force to input force is called the...
mechanical advantage
72
Type 1 lever
- fulcrum is betwen force and loas - seesaw - push down on onw end and lift load at other - increase force at expense of distance - directions of input and output are opposite
73
Type 2 lever
- load is between fulcrum and input force - to lift load, you lift end of lever - force on load is increased at expense of distance - forces have same direction
74
Type 3 lever
- fulcrum is at one end and load is at other - input force is applied between them - bicep muscles to arms - increases distance at expense of force - biceps move short distance, arms move longer distance - input and output forces are no the same side of the fulcrum, i.e. have same direction
75
pulley
a kind of lever that can be used to change the direction of a force
76
Can a pulley or system of pulleys multiply the force?
Yes
77
The mechanical advantage for simple pulley is the same as the number of __________________________________.
strands of rope that actually support the load
78
Can a machine be 100% efficient?
No
79
In any machine, some energy is _________into ________ or _________kinetic energy, which makes the machine warmer.
transformed; atomic; molecular
80
The efficiency of a machine is...
the ratio of useful energy output to total energy input, or the percentage of the work input that is converted to work output
81
Is an inclined plane a machine?
Yes
82
What can efficiency also be expressed as?
actual mechanical advantage/ theoretical mechanical advantage
83
Will efficiency always be a fraction less than 1?
Yes
84
An automobile is a machine that transforms _______________stored in fuel into _________________.
chemical energy; mechanical energy
85
Burning is a chemical reaction in which ______________________.
atoms combine with oxygen, and energy is released
86
Is transforming 100% of thermal energy into mechanical energy possible?
No
87
Does friction add more to the energy loss?
Yes
88
Is every living cell in every organism a machine?
Yes
89
Is there more energy stored in the molecules oin food than there is in the reaction products after the food is metabolized?
Yes
90
What is the source of practically all our energy on Earth?
The sun, nuclear, and geothermal energy
91
How is sunlight directly transformed into electricity?
Photovoltaic cells
92
Is hydrogen the least polluting of all fuels?
Yes
93
Does it take energy to make hydrogen? If so, why?
Yes, bc it is extracted from water and carbon compounds
94
Where is the most concentrated form of usable energy stored in?
Uranium and plutonium, which are nuclear fuel
95
What is geothermal energy a byproduct of?
Radioactivity in Earth's interior
96
Where is geothermal energy held?
In underground reservoirs of hot water

Preparation for Physics Final (11 decks)

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