Download ultraviolet light which of the following best illustrates the physics

Work, Energy, and Power
Forms of Ener.qy
is the mediator of all physical changesisuch as changes in speed, height,
emperat !or chemical composition.
Energy comes in many forms.
energy includes energy associated With motion and positionl
Examples include:
• kinetic energy
• gravitational potential energy
• elastic potential energy
lÿ-ÿ.,,(/[ÿoiÿ,#ÿ,!7ÿiÿ,ÿ energy includes allforms of electromagnetic radiation. Examples include
• visible light
infrared radiation
ultraviolet light
microwaves
radio waves
o
x-rays
Jÿ_ (J.JY'
energy comes from the forces that hold the atomic nucleus together.
y change in an atom's nucleus absorbs or releases nuclear energy.
Nuclear energy is the energy source for the Sun and stars.
! energy is carried by electric currents.
Electrical energy is clean, moves easily through wires, and is a key energy resource in human
technology.
Electrical energy must be derived from other forms of energy, such as nuclear or chemical energy.
' 9ÿ%ÿ ÿ'Gÿ, iÿ _ energy is energy stored in the bonds between atoms.
When chemical bonds are changed through chemical reactions, chemical energy is released.
Chemical energy is found in foods and fuels.
'ÿ ÿiÿ iÿ ,!ÿ,ÿ,i},, i! energy is energy due to temperature.
An object at a higher temperature has more thermal energy than if it was at a lower temperature.
The thermal energy also depends on the mass and material of the object.
Energy is measured in ÿiiÿ tÿ}ÿ (L.J!.ÿ
•
which of the following best illustrates the physics definition of energy?
A. "1 don't have the energy to get that done today."
"Our team needs to be at maximum energy for this game:"
"The height of her leaps takes more energy than anyone else's."
'
I"
D. "That performance was so exhilarating you could feel the energy in theaudlence.
Work, Energy, and Power
2. Which statement below provides a correct practical definition of energy?
A. Energy is a quantity that can be created or destroyed.
B. Energy is a measure of how much money it takes to produce a product.
C. The energy of an object can never change. It depends on the size and weight of an object.
Energy causes matter to change and determines how much change occurs.
Match each event with the correct form of energy.
.
I. kinetic
!1. gravitational potential
!!!. elastic potential IV. thermal
V. electrical
VI. chemical
Ice melts when placed in a cup of warm water.
Campers use a tank of propane gas on their trip.
.4_
A car travels down a level road at 25 m/s.
A bungee cord causes the jumper to bounce upward.
The weightlifter raises the barbell above his head.
A spark jumps from the girl's finger to the doorknob ....... after she scuffs her feet on the
wool rug.
Y__
Work
The work done on an object equals the force on the object multiplied by the distance the object moves in the
direction of the force.
W- - Fd
Work is done by forces that change the motion of an object.
"A A force of 1 newton acting over 1 meter does one joule of physical workÿ
P; w(©
How much work do you do on a wall if you push on it with a force of 100 N? ÿ = ÿo)ÿ ÿ Iÿ t ÿb} ÿ ÿ.ÿ Io
_
Draw the FBD for a 10 kg crate being pulled al g a level surface.
.....
.ÿ,ÿ/GI_
:'
'
For each force actingon this crate, decide if it is doing work and explain.
.......
ÿ
':l "gÿ C: "
Work, Energy, and Power
Two robots apply a combined horizontal force of 200 N to a 40 kg box, causing it to slide 5.0 meters.
The force of friction between the floor and the box is 50 N.
How much work is done by each force acting on the box?
Gravity: ÿ ÿ'ÿ ÿ;ÿ°Normal force: 0 ',ÿJ..ÿ,.
Applied force: +\50 0 ÿ:ÿ00ÿ,b
Friction: ÿ-ÿ ÿ ,3;ÿ ÿ.} \cÿ-:.
All physical changes are due to changes in J ÿjÿh. ÿ\ÿ.
When work is done, energy is transferred from one o6je&)to another, or transformed from one type of
energy to another.
The amount of work done equals the amount of enerqy transformed.
1. How is the joule composed of the units for force and distance?
2. What do each of the symbols mean in this equation: W = Fd?
3. A 75 N force acts on an object over a distance of 10 meters, in the same direction as the
object moves. How much work is done?
IKinetic Energy
The kinetic energy of a moving object is one half of the
product of its mass multiplied by the square of its velocity.
Kinetic energy is energy due to ÿ ÿ¢!. :ÿ.^ÿ
1
---- "--mY
2
A 1 liter water bottle (1 kg) moving at 1 m/s (2.4 mph) has a kinetic energy of 0.5 joules.
What is the speed of a 2000 kg car thatÿ enerÿz_ÿ500,000 joules?
The kinetic energy increases as the squareof the speed."
If the speed triples, how does the kinetic energy change?
,
Work, Energy, and Power
A cart has 10 joules of kinetic energy.
If its mass doubles AND its velocity doubles, how much kinetic energy does it have?/f:ÿ.W
1. How much kinetic energy does a 1.0 kg mass have when traveling at a speed of 30 m/s?
,
How much kinetic energy does the mass have when traveling at twice this speed?
3. What is the mass of an object that has a kinetic energy of 500 joules and a speed of 25 m/s?
Gravitational potential energy
The change in gravitational potential energy of an
object is its mass multiplied by "g" and by the change in height.
PE = ngh
........ ÿ.= . . ....... . e W_,:ÿ<_ t.:C,
This heavy container has been raised up above ground level.
Due to its height, it has stored energyÿgravitational potential energy.
if the container is released, the" ÿbr4ÿ{ 2 ÿ-L.4 ÿ'4 ÿ:OrI&g° t :ÿ'ÿ"i!,7:ÿ
of the container increases, its potential energy will also increase.
of the container increases, its potential energy will also increase.
Work, Energy, and Power
PE- - mgh
The 0ÿ\ÿ&,),/ÿk::ÿq jÿ'ÿ,, (kÿ '?ÿtiÿ(ÿfÿlii,,k!ÿ,ÿ ÿ:ÿ,ÿ,4,ÿ ÿ,,,,:ÿ,,ÿ, 4 of a n object is the ÿ[\ÿ (ÿ_ &ÿ
m in kfletgrams multiplied by the Ckÿ,#,:Scÿ,ÿ4-I,ÿ;ÿ;J dueto grÿJ{titÿ/g (which is 9.8 m/s2 nearEarth's
surface), multiplied by the _ÿ,: ÿ :ÿc4 h in meters.
How can you give an object gravitational potential energy? ÿ,,JL ÿ6ÿv'q"ÿ--- +ÿ ÿ (ÿL 0 V,J ÿ,%
,ÿ " ' " :,
i<{:"!c t 7<ÿ.+<,ÿ .... ÿ. ! ¢-ÿ-ÿt.. +jÿ,,+-.'ÿ, +
0
<J "I
OÿoV,--ÿ° ' "",?ÿc \t ÿ':ÿ"
. -
How much energy does it take to raise a 70 kg (154 Ib) person one meter off the ground?
A set of identical twins wants to get to the top of a mountain.
• One twin hikes up a winding trail.
° The second twin takes the secret elevator straight to the top.
Which twin has the greatest potential energy at the top?
"
ÿ!,'
0 7,, =c
'<
,
pÿ,
Power
AE
The power of a system is the energy transformed, divided by the time it takes.
At
W
At
or°°ÿ
The power of a system is the work done divided by the time it takes to do the
work.
Work, Energy, and Power
A 1200 kg sports car accelerates from 0 to 60 mph (27 m/s) in 5.0 seconds.
A typical car of equal mass takes 8.0 seconds to do the same thing.
So what's the difference? ÿ ÿ ÿI ÿ ÿ \ ÿ (ÿ3)ÿ;Iÿ ÿ ÿ T ÿ'ÿ't4ÿUÿ,ÿ!ÿ ©ÿA.ÿi ÿ ÿ ÿi.ÿ;'ÿ%ÿ "ÿ)
Both cars convert the ÿ_q"C,oÿC&ÿ energy of their gasoline into the same amount of ÿ\ÿ%,ÿi ÿnergy,
but the sports car converts energy at a faster rate. It converts more -dÿC_Afÿ every second.
Any event in which energy is transformed involves power.
Power is typically measured in __ÿ',.JÿJÿ'ÿ
Power is the "(ÿk:ÿ'ÿ:#
at which work is done.
Lifting a ball quickly requires more power than lifting it slowly.
An elephant lifts a 300 kg log to a height of 3.0 meters in a time of 4.0 seconds. How much power is
required?
A 1200 kg sports car accelerates from 0 to 60 mph (27.0 m/s) in 5.20 seconds. What is the average
power developed? ÿID ÿfÿ£ÿ ÿ ÿ'ÿ ÿ'ÿ t4
What other unit often used for the power of a car? The horsepower!
One horsepower equals ÿ}ÿtÿ watts.
A toaster oven operating at 800 watts takes one and a half minutes to toast a bagel. How much
L
energy is this? ,ÿ,ÿ) ÿ\ÿd =-ÿ?'ÿDÿ:.ÿ ÿ__-ÿ ÿL-t-ÿÿ ÿZÿL)ÿ'ÿb)=ÿ2-ÿ&ÿO,ÿ 6"f "ÿ'ÿt .ÿ
1. What do each of the symbols mean in this equation? ÿd ÿ'!\j
\"zi r' ÿ "*' ÿ"
2. An engine has an output energy of 2,400 J in 10 seconds. What is its average power in watts?
6
Work, Energy, and Power
Systems and Energy
For any closed system that undergoes a change, the A1[bÿk \
same as the JCOJÿ\ energy after the change.
energy before the change is the
Law of Conservation of Enerqy
Energy can never be created nor destroyed, only changed from one form to another.
is a group of interacting objects and influences, such as forces.
In an O Cÿ,ÿ/ÿ. system, energy and matter can pass through the imaginary system boundary and
leave the svstem., __...
"
'
,.,I, ÿ.ÿ,,ÿ ÿÿ.',, ÿ ÿ
, ';',,ÿ :.ÿ,ÿ
.....
Mÿ,v't ' ÿ
Within a closed system, energy can be exchanged or transformed, but the ÿ OÿTc-d
....
'?<','*
energy
remains constant.
A frictionless rollercoaster provides a good example of a closed system. The t{ÿ'ÿ,C (ÿ_ ,'tÿ %ÿ ÿ1' ÿ.Jÿ ' ÿ ÿ ÿ ÿ ÿ ÿ{ÿ ÿjÿ ÿÿ
,, i,ÿ vÿJ.ÿ,htlÿ.ÿ
of this system is conserved.
Conservation.of energy.on; a. rolliercoaster " ; .:. '
Closed system
E; + Eÿ =constant',
Work, Energy, and Power
1. Asystem in
physics is best described as...
a collection of related objects and interactions.
the masses and velocities of a collection of objects.
C. the masses and velocities of a collection of objects, and the forces that act on them.
D. the objects within a volume that you are interested in
2. A large bird with a mass of 1.0 kg is flying at a height of 10 meters, at a speed of 10 m/s. What
is the mechanical energy of the bird?
>
........
ÿ. ÿ,, ÿ,,, ÿ,, ,ÿ,,ÿ . ÿ
t j
It,/--
Work-Energy Theorem
Formula"
The total work done on an object equals its change in .
'<.>ÿ
Newton's second law is a fundamental statement that relates the net force on an object to its
acceleration.
,ÿk <' 7ÿ tÿ<,
The work-energy theorem is a fundamental statement that relates the net-workÿwork done by the
net forceÿto changes in an object's energy.
A box is at rest on a frictionless table top>The force of gravity and the normal force from the table do
zero work on the box. The ÿ,ÿ_qv
ÿVÿ()_ÿ,
is zero, so the box does not gain or lose
kinetic energy. That makes sense!
A net force is applied to a box that is initially at rest on a frictionless surface. The force does 200
joules of work. What is the resulting kinetic energy of the box?
A 10 kg box is initially at rest. A 50 N net force is applied to the box for a distance of 5.0 meters.
What is the resulting speed of the box?
A. ÿi,ÿ l.
;ÿ .... "