QBManager

WAVES

173078 A source producing sound of frequency $170 Hz$ is approaching a stationary observed with a velocity of $17 {ms}^{- 1}$ . The apparent change in the wavelength of sound heard by the observer is (speed of sound in air $= 340 {ms}^{- 1}$ )

1

0.1 m

2

0.2 m

3

0.4 m

4

0.5 m

Explanation:

A Given that,
$V = 340 {ms}^{- 1}, V_{s} = 17 m / s$
$f = 170 Hz$
wave length of sound,
$λ = \frac{V}{n} = \frac{340}{170} \Rightarrow 2 m$
Apparent frequency
$f^{'} = (\frac{v}{v - v_{s}}) f$
$f^{'} = \frac{340}{340 - 17} \times 170$
$f^{'} = 178.9 Hz$
$λ^{'} = \frac{V}{f^{'}} = \frac{340}{178.9} = 1.9$
$λ - λ^{'} = 2 - 1.9 \Rightarrow 0.1 m$
$λ - λ^{'} == 0.1 m$

EAMCET - 2000

WAVES

173079 An observer is standing $500 m$ away from a vertical hill. Starting between the observer and the hill, a police van sounding a siren of frequency $1000 Hz$ moves towards the hill with a uniform speed. If the frequency of the sound heard directly from the siren is $970 Hz$ , the frequency of the sound heard after reflection from the hill (in $Hz$ ) is about, (velocity of sound $= 300 {ms}^{- 1}$ )

1 1042

2 1032

3 1022

4 1012

Explanation:

B Sound heard directly is given by,
$f_{o} = 1000 Hz$
$f^{'} = 970 Hz$
$v = 300 {ms}^{- 1}$
$f^{'} = f_{o} (\frac{v}{v + v_{s}})$
$970 = 1000 (\frac{330}{330 + v_{s}})$
$v_{s} = 10.2 {ms}^{- 1}$
The frequency of sound reflected is given by,
$f^{''} = f_{o} (\frac{v}{v - v_{s}})$
$f^{''} = 1000 (\frac{330}{330 - 10.2})$
$f^{''} = 1000 \times 1.032$
$f^{''} = 1032 Hz$

EAMCET - 2006

WAVES

173080 A vehicle sounding a whistle of frequency 256 $Hz$ is moving on a straight road, towards a hill with a velocity of $10 {ms}^{- 1}$ . The number of beats per second observed by a person travelling in the vehicle is (velocity of sound $= 330 {ms}^{- 1}$ )

1 zero

2 10

3 14

4 16

Explanation:

D We know that,
Doppler effect equation-
$f^{'} = \frac{(v + v_{0})}{(v - v_{s})} f$
$f^{'} = (\frac{330 + 10}{330 - 10}) \times 256 = \frac{340}{320} \times 256$
$= 272 Hz$
$∴$ Number of beats $(Δ f) = f^{'} - f$
$= 272 - 256 = 16$

EAMCET - 2005

WAVES

173081 A sound wave has frequency of $2 kHz$ and wavelength of $35 cm$ . If an observer is $1.4 km$ away from the source, after what time interval could the observer hear the sound?

1

0.2 s

2

20 s

3

0.5 s

4

4 s

Explanation:

A Frequency (f) $= 2 kHz = 2000 Hz$
Wave length $(λ) = 35 cm \Rightarrow 0.35 m$
$v = f λ$
$= 0.35 \times 2000$
$= 700 m / s$
$d = 1.4 km$
$t = \frac{d}{v} = \frac{(1.4) \times 100}{700} \Rightarrow 0.2 \sec .$

NDA (I) 2014

WAVES

173078 A source producing sound of frequency $170 Hz$ is approaching a stationary observed with a velocity of $17 {ms}^{- 1}$ . The apparent change in the wavelength of sound heard by the observer is (speed of sound in air $= 340 {ms}^{- 1}$ )

1

0.1 m

2

0.2 m

3

0.4 m

4

0.5 m

Explanation:

A Given that,
$V = 340 {ms}^{- 1}, V_{s} = 17 m / s$
$f = 170 Hz$
wave length of sound,
$λ = \frac{V}{n} = \frac{340}{170} \Rightarrow 2 m$
Apparent frequency
$f^{'} = (\frac{v}{v - v_{s}}) f$
$f^{'} = \frac{340}{340 - 17} \times 170$
$f^{'} = 178.9 Hz$
$λ^{'} = \frac{V}{f^{'}} = \frac{340}{178.9} = 1.9$
$λ - λ^{'} = 2 - 1.9 \Rightarrow 0.1 m$
$λ - λ^{'} == 0.1 m$

EAMCET - 2000

WAVES

173079 An observer is standing $500 m$ away from a vertical hill. Starting between the observer and the hill, a police van sounding a siren of frequency $1000 Hz$ moves towards the hill with a uniform speed. If the frequency of the sound heard directly from the siren is $970 Hz$ , the frequency of the sound heard after reflection from the hill (in $Hz$ ) is about, (velocity of sound $= 300 {ms}^{- 1}$ )

1 1042

2 1032

3 1022

4 1012

Explanation:

B Sound heard directly is given by,
$f_{o} = 1000 Hz$
$f^{'} = 970 Hz$
$v = 300 {ms}^{- 1}$
$f^{'} = f_{o} (\frac{v}{v + v_{s}})$
$970 = 1000 (\frac{330}{330 + v_{s}})$
$v_{s} = 10.2 {ms}^{- 1}$
The frequency of sound reflected is given by,
$f^{''} = f_{o} (\frac{v}{v - v_{s}})$
$f^{''} = 1000 (\frac{330}{330 - 10.2})$
$f^{''} = 1000 \times 1.032$
$f^{''} = 1032 Hz$

EAMCET - 2006

WAVES

173080 A vehicle sounding a whistle of frequency 256 $Hz$ is moving on a straight road, towards a hill with a velocity of $10 {ms}^{- 1}$ . The number of beats per second observed by a person travelling in the vehicle is (velocity of sound $= 330 {ms}^{- 1}$ )

1 zero

2 10

3 14

4 16

Explanation:

D We know that,
Doppler effect equation-
$f^{'} = \frac{(v + v_{0})}{(v - v_{s})} f$
$f^{'} = (\frac{330 + 10}{330 - 10}) \times 256 = \frac{340}{320} \times 256$
$= 272 Hz$
$∴$ Number of beats $(Δ f) = f^{'} - f$
$= 272 - 256 = 16$

EAMCET - 2005

WAVES

173081 A sound wave has frequency of $2 kHz$ and wavelength of $35 cm$ . If an observer is $1.4 km$ away from the source, after what time interval could the observer hear the sound?

1

0.2 s

2

20 s

3

0.5 s

4

4 s

Explanation:

A Frequency (f) $= 2 kHz = 2000 Hz$
Wave length $(λ) = 35 cm \Rightarrow 0.35 m$
$v = f λ$
$= 0.35 \times 2000$
$= 700 m / s$
$d = 1.4 km$
$t = \frac{d}{v} = \frac{(1.4) \times 100}{700} \Rightarrow 0.2 \sec .$

NDA (I) 2014

WAVES

173078 A source producing sound of frequency $170 Hz$ is approaching a stationary observed with a velocity of $17 {ms}^{- 1}$ . The apparent change in the wavelength of sound heard by the observer is (speed of sound in air $= 340 {ms}^{- 1}$ )

1

0.1 m

2

0.2 m

3

0.4 m

4

0.5 m

Explanation:

A Given that,
$V = 340 {ms}^{- 1}, V_{s} = 17 m / s$
$f = 170 Hz$
wave length of sound,
$λ = \frac{V}{n} = \frac{340}{170} \Rightarrow 2 m$
Apparent frequency
$f^{'} = (\frac{v}{v - v_{s}}) f$
$f^{'} = \frac{340}{340 - 17} \times 170$
$f^{'} = 178.9 Hz$
$λ^{'} = \frac{V}{f^{'}} = \frac{340}{178.9} = 1.9$
$λ - λ^{'} = 2 - 1.9 \Rightarrow 0.1 m$
$λ - λ^{'} == 0.1 m$

EAMCET - 2000

WAVES

173079 An observer is standing $500 m$ away from a vertical hill. Starting between the observer and the hill, a police van sounding a siren of frequency $1000 Hz$ moves towards the hill with a uniform speed. If the frequency of the sound heard directly from the siren is $970 Hz$ , the frequency of the sound heard after reflection from the hill (in $Hz$ ) is about, (velocity of sound $= 300 {ms}^{- 1}$ )

1 1042

2 1032

3 1022

4 1012

Explanation:

B Sound heard directly is given by,
$f_{o} = 1000 Hz$
$f^{'} = 970 Hz$
$v = 300 {ms}^{- 1}$
$f^{'} = f_{o} (\frac{v}{v + v_{s}})$
$970 = 1000 (\frac{330}{330 + v_{s}})$
$v_{s} = 10.2 {ms}^{- 1}$
The frequency of sound reflected is given by,
$f^{''} = f_{o} (\frac{v}{v - v_{s}})$
$f^{''} = 1000 (\frac{330}{330 - 10.2})$
$f^{''} = 1000 \times 1.032$
$f^{''} = 1032 Hz$

EAMCET - 2006

WAVES

173080 A vehicle sounding a whistle of frequency 256 $Hz$ is moving on a straight road, towards a hill with a velocity of $10 {ms}^{- 1}$ . The number of beats per second observed by a person travelling in the vehicle is (velocity of sound $= 330 {ms}^{- 1}$ )

1 zero

2 10

3 14

4 16

Explanation:

D We know that,
Doppler effect equation-
$f^{'} = \frac{(v + v_{0})}{(v - v_{s})} f$
$f^{'} = (\frac{330 + 10}{330 - 10}) \times 256 = \frac{340}{320} \times 256$
$= 272 Hz$
$∴$ Number of beats $(Δ f) = f^{'} - f$
$= 272 - 256 = 16$

EAMCET - 2005

WAVES

173081 A sound wave has frequency of $2 kHz$ and wavelength of $35 cm$ . If an observer is $1.4 km$ away from the source, after what time interval could the observer hear the sound?

1

0.2 s

2

20 s

3

0.5 s

4

4 s

Explanation:

A Frequency (f) $= 2 kHz = 2000 Hz$
Wave length $(λ) = 35 cm \Rightarrow 0.35 m$
$v = f λ$
$= 0.35 \times 2000$
$= 700 m / s$
$d = 1.4 km$
$t = \frac{d}{v} = \frac{(1.4) \times 100}{700} \Rightarrow 0.2 \sec .$

NDA (I) 2014

WAVES

173078 A source producing sound of frequency $170 Hz$ is approaching a stationary observed with a velocity of $17 {ms}^{- 1}$ . The apparent change in the wavelength of sound heard by the observer is (speed of sound in air $= 340 {ms}^{- 1}$ )

1

0.1 m

2

0.2 m

3

0.4 m

4

0.5 m

Explanation:

A Given that,
$V = 340 {ms}^{- 1}, V_{s} = 17 m / s$
$f = 170 Hz$
wave length of sound,
$λ = \frac{V}{n} = \frac{340}{170} \Rightarrow 2 m$
Apparent frequency
$f^{'} = (\frac{v}{v - v_{s}}) f$
$f^{'} = \frac{340}{340 - 17} \times 170$
$f^{'} = 178.9 Hz$
$λ^{'} = \frac{V}{f^{'}} = \frac{340}{178.9} = 1.9$
$λ - λ^{'} = 2 - 1.9 \Rightarrow 0.1 m$
$λ - λ^{'} == 0.1 m$

EAMCET - 2000

WAVES

173079 An observer is standing $500 m$ away from a vertical hill. Starting between the observer and the hill, a police van sounding a siren of frequency $1000 Hz$ moves towards the hill with a uniform speed. If the frequency of the sound heard directly from the siren is $970 Hz$ , the frequency of the sound heard after reflection from the hill (in $Hz$ ) is about, (velocity of sound $= 300 {ms}^{- 1}$ )

1 1042

2 1032

3 1022

4 1012

Explanation:

B Sound heard directly is given by,
$f_{o} = 1000 Hz$
$f^{'} = 970 Hz$
$v = 300 {ms}^{- 1}$
$f^{'} = f_{o} (\frac{v}{v + v_{s}})$
$970 = 1000 (\frac{330}{330 + v_{s}})$
$v_{s} = 10.2 {ms}^{- 1}$
The frequency of sound reflected is given by,
$f^{''} = f_{o} (\frac{v}{v - v_{s}})$
$f^{''} = 1000 (\frac{330}{330 - 10.2})$
$f^{''} = 1000 \times 1.032$
$f^{''} = 1032 Hz$

EAMCET - 2006

WAVES

173080 A vehicle sounding a whistle of frequency 256 $Hz$ is moving on a straight road, towards a hill with a velocity of $10 {ms}^{- 1}$ . The number of beats per second observed by a person travelling in the vehicle is (velocity of sound $= 330 {ms}^{- 1}$ )

1 zero

2 10

3 14

4 16

Explanation:

D We know that,
Doppler effect equation-
$f^{'} = \frac{(v + v_{0})}{(v - v_{s})} f$
$f^{'} = (\frac{330 + 10}{330 - 10}) \times 256 = \frac{340}{320} \times 256$
$= 272 Hz$
$∴$ Number of beats $(Δ f) = f^{'} - f$
$= 272 - 256 = 16$

EAMCET - 2005

WAVES

173081 A sound wave has frequency of $2 kHz$ and wavelength of $35 cm$ . If an observer is $1.4 km$ away from the source, after what time interval could the observer hear the sound?

1

0.2 s

2

20 s

3

0.5 s

4

4 s

Explanation:

A Frequency (f) $= 2 kHz = 2000 Hz$
Wave length $(λ) = 35 cm \Rightarrow 0.35 m$
$v = f λ$
$= 0.35 \times 2000$
$= 700 m / s$
$d = 1.4 km$
$t = \frac{d}{v} = \frac{(1.4) \times 100}{700} \Rightarrow 0.2 \sec .$

NDA (I) 2014