Physics1101 Multiple choice

Transcript Physics1101 Multiple choice

Physics1101 Multiple choice

MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.

1) You are driving along a highway at 25 m/s when you hear the siren of an emergency vehicle traveling in the opposite direction on the other side of the highway. When the vehicle is approaching you, you hear the frequency of the siren as 2300 Hz, but when it is past you the frequency becomes 1600 Hz. What is the speed of the vehicle? The speed of sound in air is 343 m/s.

A) 30 m/s B) 41 m/s C) 32 m/s D) 37 m/s

f f

1  1 

 

v v



v o



v s

 

  343 343  25 

v s

  1600

1600



(

  343 343

343

   25

v s v s

)

  

 548800  318 1600

v s f

318

Two unknowns Solve for f Substitute in equation 2 into equation 1

1 

 

v v



v o



v s

 

1  2300

  343 343   25

v s

  

  343 343  25 

v s

  2300 ( 343 

v s

) 

368

 788900  368 2300

v s

48911800  1320200

v s

788900  368 2300

v s

 548800  318 1600

v s

318 ( 788900  2300

v s

)  368 ( 548800  1600

v s

) 250870200  731400

v s

 201958400  588800

v s

250870200  201958400  731400

v s

 588800

v s

48911800 1320200 

v s v s

 37

m s

2) A camper is about to drink his morning coffee. He pours 400 grams of coffee, initially at 75.0eC, into a 250-g aluminum cup, initially at 16.0eC. What is the equilibrium temperature of the coffee-cup system, assuming no heat is lost to the surroundings? The specific heat of aluminum is 900 J/(kg\'97K). A) 71.0eC B) 68.0eC C) 65.0eC D) 62.0eC



t co ff





t cu p

4 ( 4186 )( 75 

t f

)  (.

250 )( 900 )(

t f

 16 ) 1674 ( 75 )  1674

t f

 225

t f

 3600 125580  1674

t f

 225

t f

 3600 125580  3600  225

t f

 1674 ( 129180 225  1674 ) 

t f t f

 68 

3) If you add 1.73 MJ of heat to 700 g of water at 70eC, what is the final temperature of the steam? The latent heat of vaporization of water is 22.6 þ 10 to power of (exponent) J/kg. The specific heat of steam is 2010 J/(kg K). A) 123eC B) 143eC C) 100eC D) 147eC First find how many joules it take to bring water to boil.

MC wa ter





.

7 ( 4186 )( 100



70 )



.

7 ( 2260000 )

1669906 1730000



1669906 60094

Subtract this from the heat being supplied. Remember the heat being supplied is 1730000J Now use this to find the final temperature of the steam

MC steam





60094



 60094





60094 .

7 ( 2010 )



 42 .

71 Now solve for t f

t f



t i

 43

t f

 100  43

t f

 43  100

t f

 143

4) The intensity level of a power mower at a distance of 1.0 m is 100 dB. You wake up one morning to find that four of your neighbors are mowing their lawn 20 m from your open bedroom window. What is the intensity level in your bedroom? A) 400 dB B) 50 dB C) 80 dB D) 104 dB

 10 log

I I o

100



10 (log



log

I o

)

10  log

 log

I o

10



log



log

I o

10  log

 log( 10  1 2 )

10



log

 

12

Note that the intensity level is in db. So you will have to change it to W/m 2

1 

2 I o =1 * 10 -12 W/m 2.

2 

( 4 )(



4 (



)(.

01 )

)



2 Now you will have to change it back to db.

2  0 .

000025

W m

4

2 

0 .

0001 10



12



log

I I

 10  2

W m

 10 log 10  4 10  1 2



80

5) A 42.0-g block of ice at -15.0eC is dropped into a calorimeter containing water at 15.0eC. When equilibrium is reached, the final temperature is 8.0eC. How much water did the calorimeter contain initially? The specific heat of ice is 2090 J/(kg K) and the latent heat of fusion of water is 33.5 * 10 4 J/kg. A) 546 g B) 405 g C) 634 g D) 302 g



t ice



MH f





t icewa ter





t wa ter

(.

042 )( 2090 )( 15 )



.

042 ( 335000 )



.

042 ( 4186 )( 8 )



( 4186 )( 7 )

 16793 .

196 29302



.

573

kg M

 573

6) Two strings of identical mass per unit length are stretched with the same tension with their ends fixed, but one string is 0.33 cm longer than the other. Waves on these strings propagate at 36.4 m/s. The fundamental frequency of the shorter string is 258 Hz. What is the beat frequency when each string is vibrating at its fundamental frequency? A) 12.7 Hz B) 12.0 Hz C) 11.3 Hz D) 11.5 Hz



  1 

v f

 1  36 .

4 258  1 

.

141

L L

2 2 

0 .

0705



0 .

07384

 2 

2

2  2 

0 .

1476



0 .

0033

m f

2  

2  36 .

4 0 .

1476

2 

246 .

47

1 

2  11 .

1  1 2  1

1  1 2 (.

141 )

1 

0 .

705

7) A 400-g piece of metal at 130 o C is dropped into a cup containing 450 g of water at 15.0 o C. The final temperature of the system is 40.0 o C. What is the specific heat of the metal, assuming no heat is exchanged with the surroundings or the cup? A) 3420 J/(kg.K) B) 1310 J/(kg.K) C) 2830 J/(kg.K) D) 3780 J/(kg.K)







0 .

400

( 130  40 )  0 .

450 ( 4186 )( 40  15 )

 0 .

450 ( 4186 )( 25 ) 0 .

450 ( 110 )

 1308

kgC



8) The speed of sound through the ground is about 6.0 km/s while the speed of sound in air is 343 m/s. A very powerful explosion occurs some distance away and you feel the ground vibrate 60 seconds before you hear the sound of the explosion. How far away is the explosion? A) 20 km B) 25 km C) 22 km D) 27 km

v g ro u n d

 6 .



6000

m s t so u n d



t g ro u n d

 60

v a ir

 343

m s v g ro u n d t g ro u n d v g ro u n d t g ro u n d



v a ir t a ir



v a ir t a ir

6000 (

t g

)  343 (

t g ro u n d

 60 ) 6000

t g ro u n d

 343

t g ro u n d

 20580 ( 6000  343 )

t g ro u n d

 20580

t g ro u n d

 20580 5657

t g ro u in d

 3 .

s d



v g ro u n d t g ro u n d d

 6000 ( 3 .

64 )

 21800  22

k m

9) The wave speed in an aluminum wire with a radius of 1.00 mm is 120 m/s. What is the tension in the wire? The density of aluminum is 2.70 x 10 3 kg/m 3 . A) 112 N B) 122 N C) 427 N D) 134 N Note to solve this problem it will take a little rearranging of various formulas, so pay attention to the algebra.



T M L

M=ρV

 

T V L

V=AL



 

T AL L T



2 The lengths will cancel here and A=πr 2 .

Square both sides to get rid of the root sign.

2 



2 

2 

T T

 ( 2700 )(  )( 0 .

001 2 )( 120 2 )

 122

10) How much heat must be removed from 456 g of water at 25.0eC to change it into ice at -10.0eC? The specific heat of ice is 2090 J/(kg K) and the latent heat of fusion of water is 33.5 þ 10 to power of (exponent) J/kg. A) 153 kJ B) 210 kJ C) 57.3 kJ D) 47.7 kJ

Q Q Q

1 1 1   



.

456 ( 4186 )( 25 ) 47720

J Q

2 



t Q

2 

.

456 ( 2090 ) 10

2 

9530

J Q

3 

MH ice Q

3 

.

456 ( 335000 )

3 

152760

J Q T



1 

2 

Q T



47720



9530



152760

Q T



210010

12) A 25.0-g string is stretched with a tension of 43.0 N between two fixed points 12.0 m apart. What is the frequency of the second harmonic? A) 12.0 Hz B) 6.00 Hz C) 24.0 Hz D) 18.0 Hz

 

 1 

T m l T m l f

 1 12 43 .

0 0 .

00208

 11 .

13) A harmonic wave travels with a speed of 200 m/s and has a wavelength of 0.800 m. What is the frequency of the wave? A) 250 Hz B) 125 Hz C) 40.0 Hz D) 80.0 Hz





 200 .



250

14) One of the harmonics of a column of air closed at one end has a frequency of 448 Hz and the next higher harmonic has a frequency of 576 Hz. What is the fundamental frequency of the air column? A) 256 Hz B) 64 Hz C) 32 Hz D) 128 Hz Remember that for a closed pipe at one end it has odd harmonics

f n



1 Create 2 equations 448 

576



(



2 )

448 

1 448



1 576  (

 2 )

1 (

576  2 ) 

1 Solve for f 1 for both equations 448  7

1  64

( 7 576  2 ) 

1 

64

448

 ( 576

 2 ) (

 2 ) 448  576

448



896

896 

576

 576

 448

896 128

 7 

Substitute one equation into the other and Solve for n.

Now put this into both equations to solve for f 1