trabajo, energía y potencia. wilson

8/12/2019 trabajo, energa y potencia. wilson

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ExamName___________________________________SHORT ANSWER. Write the word or phrase that best completes each statement or answers the question.

1)


2/302

What distinguishes work done by conservative versus nonconservative forces?

1)

_____________

TRUE/A!SE. Write "T" i# the statement is true and "" i# the statement is #alse.

2)


3/302

Work is a vector quantity

2)

_______

!)


4/302

"he work required to stretch a s#ring changes $inear$y with the amount of stretch

!)

_______

%)


5/302

&inetic energy is a sca$ar quantity

%)

_______

')


6/302

&inetic energy is #ro#ortiona$ to mass

')

_______

()


7/302

&inetic energy is #ro#ortiona$ to s#eed

()

_______

)


8/302

*rob$ems invo$ving a non-conservative force cannot be so$ved because there is no definab$e #otentia$ energy

)

_______

$U!T%&!E 'HO%'E. 'hoose the one alternati(e that best completes the statement or answers the question.

+)


9/302

,an work be done on a system if there is no motion?

+)

_______-)


10/302

.es/ since motion is on$y re$ative0)


11/302


12/302

.es/ if an externa$ force is acting on the system)


13/302

No/ since work invo$ves a non-ero dis#$acementE)


14/302

No/ since a system which is not moving has no energy

3)


15/302

Which of the fo$$owing is not a unit of work?

3)

_______-)


16/302

&w-h

0)

4

,)

&g-m5s

)

W-s

E)

N-m

16)


17/302

"he area under the curve/ on a 7orce-#osition 87-x) gra#h/ re#resents

16)

______-)


18/302

kinetic energy0)


19/302

friction,)


20/302

work)


21/302

#owerE)


22/302

efficiency

11)


23/302

"wo men/ 4oe$ and 4erry/ #ush against a wa$$ 4erry sto#s after 16 min/ whi$e 4oe$ is ab$e to #ush for '6 min $onger ,om#are the workthey do

11)

______-)


24/302

4erry does '69 more work than 4oe$0)


25/302

4oe$ does '9 more work than 4erry,)


26/302

4oe$ does '69 more work than 4erry)


27/302

4oe$ does 2'9 more work than 4erryE)


28/302

Neither of them do any work

12)


29/302

Work done by :"-";, 7


30/302

a$ong the surface0)


31/302

ero,)


32/302

#ositive)


33/302

#er#endicu$ar to the surfaceE)


34/302


35/302

.ou throw a ba$$ straight u# ,om#are the sign of the work done by gravity whi$e the ba$$ goes u# with the sign of the work done bygravity whi$e it goes down

1!)

______-)


36/302


37/302

Work u# is +/ and the work down is -

)

Work u# is -/ and the work down is +

1%)


38/302

=n a #$ot of 7 vs x/ what re#resents the work done by the force 7?

1%)

______-)


39/302

the maximum 7 times minimum x0)


40/302

the $ength of the curve,)


41/302

the area under the curve)


42/302


43/302

the #roduct of the maximum force times the maximum x

1')


44/302

,onsider an idea$ e$astic s#ring "he s#ring constant is

1')

______-)


45/302

#ro#ortiona$ to the mass attached to the s#ring0)


46/302


47/302

#ro#ortiona$ to dis#$acement from equi$ibrium)


48/302

inverse$y #ro#ortiona$ to the dis#$acementE)


49/302

none of the other answers

Use Figure 5-1 below to answer the following question(s).

i)ure *-+

1()


50/302

Which of the gra#hs above i$$ustrates >ookes @aw?

1()

______-)


51/302

gra#h a0)


52/302

gra#h b,)


53/302

gra#h c)


54/302

gra#h dE)


55/302

none of the above

1)


56/302

"he work energy theorem says

1)

______-)


57/302

fina$ kinetic energy #$us the net work done is the initia$ kinetic energy0)


58/302

the net work done is equa$ to the initia$ kinetic energy $ess the fina$ energy,)


59/302

the net work done #$us the initia$ kinetic energy is the fina$ kinetic energy)


60/302

the net work done #$us the fina$ kinetic energy is the initia$ kinetic energyE)


61/302

the net work done minus the initia$ kinetic energy is the fina$ kinetic energy

1+)


62/302

,ar 4 moves twice as fast as car &/ and car 4 has ha$f the mass of car & "he kinetic energy of car 4/ com#ared to car & is

1+)

______-)


63/302

2 to 1

0)

the same

,)

to 1

)

1 to 2

E)

% to 1

13)


64/302

;f both the mass and the ve$ocity of a ba$$ are tri#$ed/ the kinetic energy is increased by a factor of

13)

______-)


65/302


66/302

- truck weighs twice as much as a car/ and is moving at twice the s#eed of the car Which statement is true about the trucks kineticenergy 8&) com#ared to that of the car?

26)

______-)


67/302

"he truck has twice the & of the car0)


68/302

"he truck has + times the & of the car,)


69/302

"he truck has times the & of the car)


70/302

-$$ that can be said is that the truck has more &E)


71/302

"he truck has % times the & of the car

21)


72/302


73/302

times as much0)


74/302

! times as much,)


75/302

% times as much)


76/302


77/302

the same

22)


78/302

.ou and your friend want to go to the to# of the Eiffe$ "ower .our friend takes the e$evator straight u# .ou decide to wa$k u# thes#ira$ stairway/ taking $onger to do so ,om#are the gravitationa$ #otentia$ energy 8A) of you and your friend/ after you both reach theto#/ assuming that you and your friend have equa$ masses

22)

______-)


79/302

0oth of you have the same amount of #otentia$ energy0)


80/302

.our friends A is greater than your A/ because she got to the to# faster,)


81/302

;t is im#ossib$e to te$$/ since the times and distances are unknown)


82/302

.our A is greater than your friends A/ because you trave$ed a greater distance in getting to the to#

2!)


83/302

;s it #ossib$e for a system to have negative #otentia$ energy?

2!)

______-)


84/302

No/ because this wou$d have no #hysica$ meaning0)


85/302

.es/ as $ong as the tota$ energy is #ositive,)


86/302

.es/ as $ong as the tota$ energy is negative)


87/302

.es/ since the choice of the ero of #otentia$ energy is arbitraryE)


88/302

No/ because the kinetic energy of a system must equa$ its #otentia$ energy

2%)


89/302


90/302

& decreases/ and A decreases0)


91/302


92/302

& decreases/ and A increases)


93/302

& and A remain constantE)


94/302

& increases/ and A increases

2')


95/302


96/302

is equa$$y divided between kinetic energy and #otentia$ energy0)


97/302

can never be negative,)


98/302

is constant on$y if conservative forces act)


99/302


100/302

is constant on$y if nonconservative forces act

2()


101/302

&ing &ong fa$$s from the to# of the Em#ire :tate 0ui$ding/ through the air 8air friction is #resent)/ to the ground be$ow >ow does hiskinetic energy 8&) Bust before striking the ground com#are to his #otentia$ energy 8A) at the to# of the bui$ding?

2()

______-)


102/302

& is equa$ to A

0)

& is greater than A,)


103/302

& is $ess than A

)

;t is im#ossib$e to te$$

Use Figure 5-2 below to answer the following question(s).

i)ure *-,

2)


104/302

;n 7igure '-2/ showing a #endu$um/ at what #osition is the #otentia$ energy maximum?

2)

______-)


105/302

-

0)

0

,)

,

2+)


106/302

;n 7igure '-2/ showing a #endu$um/ at what #osition is the kinetic energy maximum?

2+)

______-)


107/302

-

0)

0

,)

,

A ball is released, from rest, at the left side of the loop-the-loop, at the height, h, as shown in Figure 5-3.

i)ure *--

23)


108/302


109/302


110/302


111/302

2ow much workdid the squirre$ do during that 16 s?

%()

______-)


153/302

'6 4

0)

2' 4

,)

ero

)

22 4

E)

12' 4

%)


154/302

"he resu$tant force you exert whi$e #ressing a key on the keyboard of your new com#uter/ for a 16-s #eriod/ is #$otted in 7igure '-'

i)ure *-*

>ow much work did you do during this 1-s interva$?%)

______-)


155/302

-2' 4

0)

12' 4

,)

'6 4

)

ero

E)

22 4

%+)


156/302


157/302

%3 N5cm0)


158/302

66626 N5cm,)


159/302

'6 N5cm)


160/302

626 N5cmE)


161/302

26 N5m

%3)


162/302

- s#ring is characteried by a s#ring constant of (6 N5m >ow much #otentia$ energy does it store/ when stretched by 16 cm?

%3)

______-)


163/302

(6 G4

0)

(6 4

,)

666! 4

)

6! 4

E)

(66 4

'6)


164/302

.ou $ift a 16 $b #hysics book u# in the air a distance of 1 ft/ at a constant ve$ocity of 6' ft5s "he work done by gravity is

'6)

______-)


165/302

+' ft$b

0)

ero

,)

-' ft$b

)

-16 ft$b

E)

+16 ft$b

!"# "he following question(s) refer(s) to the $%&lone, the famous roller &oaster ride at $one% 'sland, shown in the set&h. Assume

no fri&tion.

i)ure *-

'1)


166/302


167/302

62' F4

0)

' k4

,)

6%3 F4

)

!2 k4

E)

'6 k4

'2)


168/302


169/302


170/302


171/302

2

0)

ero

,)

%

)

15

E)

'%)


172/302


173/302

6%3 &m5s

0)

63+ &m5s

,)

!1 m5s

)

3+ m5s

E)

22 m5s

'')


174/302

- toy rocket/ weighing 16 N/ b$asts off from ground $eve$ -t the exact to# of its traBectory/ its energy is 1%6 4 "o what vertica$height does it rise?

'')

______-)


175/302

1% m

0)

1% km

,)

612 km

)

1% m

E)

12 m

'()


176/302

-ssuming neg$igib$e friction/ what s#ring constant wou$d be needed by the s#ring in a I0-0 gunI to fire a 16 gram #e$$et to a heightof 166 meters if the s#ring is initia$$y com#ressed 16 cm?

'()

______-)


177/302

26 N5m0)


178/302

26 N5m,)


179/302

26 N5cm)


180/302

266 N5mE)


181/302

26 N5cm

')


182/302

;f a s#ring-o#erated gun can shoot a #e$$et to a height of 166 m on Earth/ how high cou$d the #e$$et rise if fired on the moon?

')

______-)


183/302

!(6 km

0)

!(66 m

,)

166 m

)

1( m

E)

(66 m

'+)


184/302

- sim#$e #endu$um/ consisting of a mass m/ is attached to the end of a 1 yd $ength of string/ as shown in 7igure '-

i)ure *-0

;f the mass is he$d out horionta$$y/ and then re$eased from rest/ its s#eed at the bottom of the swing is about'+)

______-)


185/302

% m5s

0)

16 m5s

,)

2 m5s

)

!6 m5s

E)

1! m5s

'3)


186/302

What is the minimum energy needed to $ift 16 kg to a height of 266 km and to give it a s#eed of +6 km5s? 8Neg$ect the sma$$decrease of IgI over that distance)

'3)

______-)


187/302

!% "4

0)

!% 4

,)

!% F4

)

!% J4

E)

!% k4

(6)


188/302

- boy re$eases his 26 kg toy/ from rest/ at the to# of a s$iding-#ond inc$ined at 26C above the horionta$ What wi$$ the toys s#eed beafter s$iding %6 m a$ong the s$iding-#ond? "he coefficient of kinetic friction is 626

(6)

______-)


189/302

%% m5s

0)

22 m5s

,)

'2 m5s

)

!6 m5s

E)

!' m5s

(1)


190/302

- !6 N stone is dro##ed from a height of 16 m/ and strikes the ground with a ve$ocity of 1! m5s What average force of air frictionacts on it as it fa$$s?

(1)

______-)


191/302

61! &N

0)

12 N

,)

23 N

)

%1 N

E)

2 N

(2)


192/302

- skier/ of mass (6 kg/ #ushes off the to# of a friction$ess hi$$ with an initia$ s#eed of %6 m5s >ow fast wi$$ she be moving afterdro##ing 16 m in e$evation?

(2)

______-)


193/302

1' m5s

0)

626 km5s

,)

16 m5s

)

%3 m5s

E)

61' km5s

(!)


194/302

- 16 kg f$ash$ight fa$$s to the f$oor -t the #oint during its fa$$ when it is 66 m above the f$oor/ its #otentia$ energy exact$y equa$s itskinetic energy >ow fast is it moving?

(!)

______-)


195/302

1% m5s

0)

3+ m5s

,)

(3 m5s

)

! m5s

E)

%' m5s

i)ure *-1

(%)


196/302

"he force that a squirre$ exerts on a nut it has found is observed over a 16 second interva$/ as shown in 7igure '-+ What was theaverage #ower exerted by the squirre$?

(%)

______-)


197/302

22 W

0)

'6 W

,)

ero

)

2' W

E)

1! W

(')


198/302

Fy battery charger uses 12 watts -t (6 cents #er ki$owatt-hour/ how much does it cost to charge batteries for 2% hours?

(')

______-)


199/302

6% cents

0)

1 cents

,)

2! cents

)

1% cents

E)

62+ cents

SHORT ANSWER. Write the word or phrase that best completes each statement or answers the question.

(()


200/302

- #assenger at an air#ort #u$$s a ro$$ing suitcase by its hand$e ;f the force used is 16 N and the hand$e makes an ang$e of 2'C to thehorionta$/ what is the work done by the #u$$ing force whi$e the #assenger wa$ks 266 m?

(()

_____________

()


201/302

- father #u$$s his young daughter on a s$ed with a constant ve$ocity on a $eve$ surface through a distance of 16 m/ as i$$ustrated in 7ig'2!a ;f the tota$ mass of the s$ed and the gir$ is !' kg and the coefficient of kinetic friction between the s$ed runners and the snow is626/ how much work does the father do?

i)ure *.,- 2a3

()

_____________

(+)


202/302

- '66-kg/ $ight-weight he$ico#ter ascends from the ground with an acce$eration of 266 m5 =ver a '66-s interva$/ what is 8a) thework done by the $ifting force/ 8b) the work done by the gravitationa$ force/ and 8c) the net work done on the he$ico#ter?

(+)

_____________

(3)


203/302

;f a s#ring is com#ressed 26 cm from its equi$ibrium #osition and then com#ressed an additiona$ 26 cm/ how much more work isdone in the second com#ression than in the first? Ex#$ain

(3)

_____________

6)


204/302

"o measure the s#ring constant of a certain s#ring/ a student a##$ies a %6-N force/ and the s#ring stretches by '6 cm What is thes#ring constant?

6)

_____________

1)


205/302

,om#ute the work done by the variab$e force in the gra#h ofF versus in 7ig '2( K*int "he area of a triang$e isA = a$titude baseL

i)ure *.,

1)

_____________

2)


206/302

.ou want to decrease the kinetic energy of an obBect as much as you can .ou can do so by either reducing the mass by ha$f orreducing the s#eed by ha$f Which o#tion shou$d you #ick/ and why?

2)

_____________

!)


207/302

- 2'-g bu$$et trave$ing at !'6 m5s hits a tree and s$ows uniform$y to a sto# whi$e #enetrating a distance of 12 cm into the trees trunkWhat force was exerted on the bu$$et in bringing it to rest?

!)

_____________

%)


208/302

- 1266-kg automobi$e trave$s at 36 km5h 8a) What is its kinetic energy? 8b) What net work wou$d be required to bring it to a sto#?

%)

_____________

')


209/302

;f the work required to s#eed u# a car from 16 km5h to 26 km5h is '6 4/ what wou$d be the work required to increase the carMss#eed from 26 km5h to !6 km5h?

')

_____________

()


210/302

"wo cars trave$ from the bottom to the to# of a hi$$ by different routes/ one of which has more twists and turns -t the to#/ which hasmore #otentia$ energy?

()

_____________

)


211/302

- 626-kg stone is thrown vertica$$y u#ward with an initia$ ve$ocity of ' m5s from a starting #oint 12 m above the ground 8a) Whatis the #otentia$ energy of the stone at its maximum height re$ative to the ground? 8b) What is the change in the #otentia$ energy of thestone between its $aunch #oint and its maximum height?

)

_____________

+)


212/302

- 166-kg b$ock 8+) is on a f$at friction$ess surface 87ig '!6) "his b$ock is attached to a s#ring initia$$y at its re$axed $ength 8s#ringconstant is '66 N5m) - $ight string is attached to the b$ock and runs over a friction$ess #u$$ey to a %'6-g dang$ing mass 8m) ;f thedang$ing mass is re$eased from rest/ how far does it fa$$ before sto##ing?

i)ure *.-4

+)

_____________

3)


213/302

- ro$$er coaster trave$s on a friction$ess track as shown in 7ig '!1 8a) ;f the s#eed of the ro$$er coaster at #oint - is what is its s#eedat #oint 0? 8b) Wi$$ it reach #oint ,? 8c) What minimum s#eed at #oint - is required for the ro$$er coaster to reach #oint ,?

i)ure *.-+

3)

_____________

+6)


214/302

- 2+-kg chi$d initia$$y at rest s$ides down a #$ayground s$ide from a height of !6 m above the bottom of the s$ide ;f her s#eed at thebottom is 2' m5s/ what is the work done by nonconservative forces?

+6)

_____________

+1)


215/302

- hiker #$ans to swing on a ro#e across a ravine in the mountains/ as i$$ustrated in 7ig '!!/ and to dro# when she is Bust above the faredge 8a) -t what horionta$ s#eed shou$d she be moving when she starts to swing? 8b) 0e$ow what s#eed wou$d she be in danger offa$$ing into the ravine? Ex#$ain

i)ure *.--

+1)

_____________

+2)


216/302

- gir$ consumes +% 4 82666 food ca$ories) of energy #er day whi$e maintaining a constant weight What is the average #owershe #roduces in a day?

+2)

_____________

+!)


217/302

- construction hoist exerts an u#ward force of '66 N on an obBect with a mass of '6 kg :tarting from rest/ determine the #ower thehoist exerted to $ift the obBect vertica$$y for 16 s under these conditions

+!)

_____________


218/302


219/302

Work done by a conservative force is inde#endent of the obBects #ath and the work on$y de#ends u#on the initia$ and fina$ #ositionsWork done by nonconservative forces is #ath de#endent

2)


220/302


221/302

7-@:E

%)


222/302

"


223/302

"


224/302

7-@:E

)


225/302

7-@:E

+)


226/302

3)


227/302

,

16)


228/302

,

11)


229/302

E

12)


230/302

0

1!)


231/302

1%)


232/302

,

1')


233/302


234/302


235/302

,

1+)


236/302

-

13)


237/302

0

26)


238/302

0

21)


239/302

,

22)


240/302

-

2!)


241/302

2%)


242/302

0

2')


243/302

,

2()


244/302

,

2)


245/302

,

2+)


246/302

-

23)


247/302

0

!6)


248/302

,

!1)


249/302

E

!2)


250/302

,

!!)


251/302

!%)


252/302

0

!')


253/302

!( 4ou$es

!()


254/302

'6 N

!)


255/302

8a) 2 cm8b) 2! m5s

!+)


256/302

D%6!

!3)


257/302

D1 and (6' 4ou$es

%6)


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8a) 62' k48b) 612 kW8c) same work but #ower doub$es

%1)


259/302

8a) (!2 k48b) 2+ watts8c) 6!+' h#

%2)


260/302

0

%!)


261/302

0

%%)


262/302

%')


263/302

0

%()


264/302

0

%)


265/302


266/302

-

%3)


267/302

,

'6)


268/302

'1)


269/302

,

'2)


270/302


271/302

'%)


272/302

,

'')


273/302


274/302

E

')


275/302

E

'+)


276/302

-

'3)


277/302

,

(6)


278/302

E

(1)


279/302

(2)


280/302

-

(!)


281/302

(%)


282/302

(')


283/302

0

(()


284/302

1+66 4

()


285/302

(16 4

(+)


286/302

8a) 1%+ 4 8b) -12! 4 8c) 2'6 4

(3)


287/302

"hree times as much/ since the work de#ends on the difference of the squares of the com#ressions

6)


288/302

+6 N5m

1)


289/302

-!6 4

2)


290/302

:ince the kinetic energy de#ends on the square of the ve$ocity/ reducing s#eed by ha$f wou$d be the most efficient o#tion

!)


291/302

-1! N

%)


292/302

8a) !+ 4 8b) -!+ 4

')


293/302

8a) +! 4

()


294/302

:ame #otentia$ energy

)


295/302

8a) +6 4 8b) '( 4

+)


296/302


297/302

8a) 11 m5s 8b) no 8c) m5s

+6)


298/302

-% 4

+1)


299/302

8a) at $east 23 m5s 8b) -ny sma$$er s#eed than 23 m5s wi$$ resu$t in $ess distance trave$ed over the ravine/ due to the conservation ofenergy

+2)


300/302

3 W

+!)


301/302

'66 W


302/302

Documents

trabajo, energía y potencia. wilson