QBManager

PHXI15:WAVES

354693 A toy-car, blowing its horn, is moving with a steady speed of $5 m / s$ , away from a wall. An observer, towards whom the toy car is moving, is able to hear 5 beats per second. If the velocity of sound in air is $340 m / s$ , the frequency of the horn of the toy car is close to :

1

680 H z

2

510 H z

3

340 H z

4

170 H z

Explanation:

From Doppler's effect
$f (direct) = f (\frac{340}{340 - 5}) = f_{1}$
Frequency received the wall $= \frac{340}{340 + 5}$
Frequency received by the person from the wall is $f ($ from wall $) = f (\frac{340}{340 + 5}) = f_{2}$
Beats $= (f_{1} - f_{2})$
$5 = f (\frac{340}{340 - 5} - \frac{340}{340 + 5})$
$\Rightarrow f = 170 H z$

JEE - 2016

PHXI15:WAVES

354694 A bat flies at a steady speed of $4 m s^{- 1}$ emitting a sound of $f = 90 \times 10^{3}$ . It is flying horizon tally towards a vertical wall. The frequency of the reflected sound as detected by the bat will be (Take velocity of sound in air as $330 m s^{- 1}$ )

1

88.1 \times 10^{3} H z

2

87.1 \times 10^{3} H z

3

92.2 \times 10^{3} H z

4

89.1 \times 10^{3} H z

Explanation:

Here, the bat is a source of sound and the wall is an observer at rest.
$∴$ Frequency of sound reaching the wall is
$f^{'} = \frac{v f}{v - v_{s}} (1)$
where $v$ is the velocity of sound in air and $v_{s}$ is velocity of source.
On reflection, the wall is the source of sound of frequency $f^{'}$ at rest and bat is an observer approaching the wall with speed
$v_{0} = v_{s} = 4 m s^{- 1}$
$∴$ Frequency heard by the bat is
$f^{''} = \frac{f^{'} (v + v_{0})}{v} = f (\frac{v + v_{0}}{v - v_{s}}) [Using (1)]$
$90 \times 10^{3} (\frac{330 + 4}{330 - 4}) = \frac{90 \times 10^{3} \times 334}{326}$
$\approx 92.2 \times 10^{3} H z .$

KCET - 2010

PHXI15:WAVES

354695 The driver of a car travelling with speed $30 m s^{- 1}$ towards a hill sounds a horn of frequency $600 H z$ . If the velocity of sound in air is $330 m s^{- 1}$ , the frequency of reflected sound as heard by driver is

1

550 H z

2

555.5 H z

3

720 H z

4

500 H z

Explanation:

When the sound is reflected from the cliff, it approaches the driver of the car. Therefore, the driver acts as an observer and both sources (car) and observer are moving.
In this case, the apparent frequency heard by the driver (observer),
$f^{'} = f (\frac{v + v_{0}}{v - v_{0}})$
Given, $f = 600 H z, v = 330 m s^{- 1}, v_{0} = 30 m s^{- 1}$
$f^{'} = 600 (\frac{330 + 30}{330 - 30}) = 720 H z$

AIIMS - 2017

PHXI15:WAVES

354696 A tuning fork of frequency $380 H z$ is moving towards a wall with a velocity of $4 m / s$ . Then the number of beats heard by a stationary listener between direct and reflected sounds will be:(velocity of sound in air is $340 m / s$ )
supporting img

1

5

2

0

3

10

4

7

PHXI15:WAVES

354697 A motor car blowing a horn of frequency $124 H z$ moves with a velocity $72 k m / h r$ towards a tall wall. The frequency of the refelected sound heard by the driver will be (velocity of sound in air is $330 m / s)$

1

132 H z

2

109 H z

3

248 H z

4

140 H z

Explanation:

The frequency of reflected sound heard by the driver
The frequency received by the wall is
$f_{1} = f (\frac{v}{v - v_{s}})$
The frequency received by the car from wall is
$f_{2} = f_{1} (\frac{v + v_{s}}{v}) \Rightarrow f_{2} = f (\frac{v + v_{s}}{v - v_{s}})$
$= 124 [\frac{330 + (72 \times 5 / 18)}{330 - (72 \times 5 / 18)}] = 140 H z$

PHXI15:WAVES

354693 A toy-car, blowing its horn, is moving with a steady speed of $5 m / s$ , away from a wall. An observer, towards whom the toy car is moving, is able to hear 5 beats per second. If the velocity of sound in air is $340 m / s$ , the frequency of the horn of the toy car is close to :

1

680 H z

2

510 H z

3

340 H z

4

170 H z

Explanation:

From Doppler's effect
$f (direct) = f (\frac{340}{340 - 5}) = f_{1}$
Frequency received the wall $= \frac{340}{340 + 5}$
Frequency received by the person from the wall is $f ($ from wall $) = f (\frac{340}{340 + 5}) = f_{2}$
Beats $= (f_{1} - f_{2})$
$5 = f (\frac{340}{340 - 5} - \frac{340}{340 + 5})$
$\Rightarrow f = 170 H z$

JEE - 2016

PHXI15:WAVES

354694 A bat flies at a steady speed of $4 m s^{- 1}$ emitting a sound of $f = 90 \times 10^{3}$ . It is flying horizon tally towards a vertical wall. The frequency of the reflected sound as detected by the bat will be (Take velocity of sound in air as $330 m s^{- 1}$ )

1

88.1 \times 10^{3} H z

2

87.1 \times 10^{3} H z

3

92.2 \times 10^{3} H z

4

89.1 \times 10^{3} H z

Explanation:

Here, the bat is a source of sound and the wall is an observer at rest.
$∴$ Frequency of sound reaching the wall is
$f^{'} = \frac{v f}{v - v_{s}} (1)$
where $v$ is the velocity of sound in air and $v_{s}$ is velocity of source.
On reflection, the wall is the source of sound of frequency $f^{'}$ at rest and bat is an observer approaching the wall with speed
$v_{0} = v_{s} = 4 m s^{- 1}$
$∴$ Frequency heard by the bat is
$f^{''} = \frac{f^{'} (v + v_{0})}{v} = f (\frac{v + v_{0}}{v - v_{s}}) [Using (1)]$
$90 \times 10^{3} (\frac{330 + 4}{330 - 4}) = \frac{90 \times 10^{3} \times 334}{326}$
$\approx 92.2 \times 10^{3} H z .$

KCET - 2010

PHXI15:WAVES

354695 The driver of a car travelling with speed $30 m s^{- 1}$ towards a hill sounds a horn of frequency $600 H z$ . If the velocity of sound in air is $330 m s^{- 1}$ , the frequency of reflected sound as heard by driver is

1

550 H z

2

555.5 H z

3

720 H z

4

500 H z

Explanation:

When the sound is reflected from the cliff, it approaches the driver of the car. Therefore, the driver acts as an observer and both sources (car) and observer are moving.
In this case, the apparent frequency heard by the driver (observer),
$f^{'} = f (\frac{v + v_{0}}{v - v_{0}})$
Given, $f = 600 H z, v = 330 m s^{- 1}, v_{0} = 30 m s^{- 1}$
$f^{'} = 600 (\frac{330 + 30}{330 - 30}) = 720 H z$

AIIMS - 2017

PHXI15:WAVES

354696 A tuning fork of frequency $380 H z$ is moving towards a wall with a velocity of $4 m / s$ . Then the number of beats heard by a stationary listener between direct and reflected sounds will be:(velocity of sound in air is $340 m / s$ )
supporting img

1

5

2

0

3

10

4

7

PHXI15:WAVES

354697 A motor car blowing a horn of frequency $124 H z$ moves with a velocity $72 k m / h r$ towards a tall wall. The frequency of the refelected sound heard by the driver will be (velocity of sound in air is $330 m / s)$

1

132 H z

2

109 H z

3

248 H z

4

140 H z

Explanation:

The frequency of reflected sound heard by the driver
The frequency received by the wall is
$f_{1} = f (\frac{v}{v - v_{s}})$
The frequency received by the car from wall is
$f_{2} = f_{1} (\frac{v + v_{s}}{v}) \Rightarrow f_{2} = f (\frac{v + v_{s}}{v - v_{s}})$
$= 124 [\frac{330 + (72 \times 5 / 18)}{330 - (72 \times 5 / 18)}] = 140 H z$

PHXI15:WAVES

354693 A toy-car, blowing its horn, is moving with a steady speed of $5 m / s$ , away from a wall. An observer, towards whom the toy car is moving, is able to hear 5 beats per second. If the velocity of sound in air is $340 m / s$ , the frequency of the horn of the toy car is close to :

1

680 H z

2

510 H z

3

340 H z

4

170 H z

Explanation:

From Doppler's effect
$f (direct) = f (\frac{340}{340 - 5}) = f_{1}$
Frequency received the wall $= \frac{340}{340 + 5}$
Frequency received by the person from the wall is $f ($ from wall $) = f (\frac{340}{340 + 5}) = f_{2}$
Beats $= (f_{1} - f_{2})$
$5 = f (\frac{340}{340 - 5} - \frac{340}{340 + 5})$
$\Rightarrow f = 170 H z$

JEE - 2016

PHXI15:WAVES

354694 A bat flies at a steady speed of $4 m s^{- 1}$ emitting a sound of $f = 90 \times 10^{3}$ . It is flying horizon tally towards a vertical wall. The frequency of the reflected sound as detected by the bat will be (Take velocity of sound in air as $330 m s^{- 1}$ )

1

88.1 \times 10^{3} H z

2

87.1 \times 10^{3} H z

3

92.2 \times 10^{3} H z

4

89.1 \times 10^{3} H z

Explanation:

Here, the bat is a source of sound and the wall is an observer at rest.
$∴$ Frequency of sound reaching the wall is
$f^{'} = \frac{v f}{v - v_{s}} (1)$
where $v$ is the velocity of sound in air and $v_{s}$ is velocity of source.
On reflection, the wall is the source of sound of frequency $f^{'}$ at rest and bat is an observer approaching the wall with speed
$v_{0} = v_{s} = 4 m s^{- 1}$
$∴$ Frequency heard by the bat is
$f^{''} = \frac{f^{'} (v + v_{0})}{v} = f (\frac{v + v_{0}}{v - v_{s}}) [Using (1)]$
$90 \times 10^{3} (\frac{330 + 4}{330 - 4}) = \frac{90 \times 10^{3} \times 334}{326}$
$\approx 92.2 \times 10^{3} H z .$

KCET - 2010

PHXI15:WAVES

354695 The driver of a car travelling with speed $30 m s^{- 1}$ towards a hill sounds a horn of frequency $600 H z$ . If the velocity of sound in air is $330 m s^{- 1}$ , the frequency of reflected sound as heard by driver is

1

550 H z

2

555.5 H z

3

720 H z

4

500 H z

Explanation:

When the sound is reflected from the cliff, it approaches the driver of the car. Therefore, the driver acts as an observer and both sources (car) and observer are moving.
In this case, the apparent frequency heard by the driver (observer),
$f^{'} = f (\frac{v + v_{0}}{v - v_{0}})$
Given, $f = 600 H z, v = 330 m s^{- 1}, v_{0} = 30 m s^{- 1}$
$f^{'} = 600 (\frac{330 + 30}{330 - 30}) = 720 H z$

AIIMS - 2017

PHXI15:WAVES

354696 A tuning fork of frequency $380 H z$ is moving towards a wall with a velocity of $4 m / s$ . Then the number of beats heard by a stationary listener between direct and reflected sounds will be:(velocity of sound in air is $340 m / s$ )
supporting img

1

5

2

0

3

10

4

7

PHXI15:WAVES

354697 A motor car blowing a horn of frequency $124 H z$ moves with a velocity $72 k m / h r$ towards a tall wall. The frequency of the refelected sound heard by the driver will be (velocity of sound in air is $330 m / s)$

1

132 H z

2

109 H z

3

248 H z

4

140 H z

Explanation:

The frequency of reflected sound heard by the driver
The frequency received by the wall is
$f_{1} = f (\frac{v}{v - v_{s}})$
The frequency received by the car from wall is
$f_{2} = f_{1} (\frac{v + v_{s}}{v}) \Rightarrow f_{2} = f (\frac{v + v_{s}}{v - v_{s}})$
$= 124 [\frac{330 + (72 \times 5 / 18)}{330 - (72 \times 5 / 18)}] = 140 H z$

PHXI15:WAVES

354693 A toy-car, blowing its horn, is moving with a steady speed of $5 m / s$ , away from a wall. An observer, towards whom the toy car is moving, is able to hear 5 beats per second. If the velocity of sound in air is $340 m / s$ , the frequency of the horn of the toy car is close to :

1

680 H z

2

510 H z

3

340 H z

4

170 H z

Explanation:

From Doppler's effect
$f (direct) = f (\frac{340}{340 - 5}) = f_{1}$
Frequency received the wall $= \frac{340}{340 + 5}$
Frequency received by the person from the wall is $f ($ from wall $) = f (\frac{340}{340 + 5}) = f_{2}$
Beats $= (f_{1} - f_{2})$
$5 = f (\frac{340}{340 - 5} - \frac{340}{340 + 5})$
$\Rightarrow f = 170 H z$

JEE - 2016

PHXI15:WAVES

354694 A bat flies at a steady speed of $4 m s^{- 1}$ emitting a sound of $f = 90 \times 10^{3}$ . It is flying horizon tally towards a vertical wall. The frequency of the reflected sound as detected by the bat will be (Take velocity of sound in air as $330 m s^{- 1}$ )

1

88.1 \times 10^{3} H z

2

87.1 \times 10^{3} H z

3

92.2 \times 10^{3} H z

4

89.1 \times 10^{3} H z

Explanation:

Here, the bat is a source of sound and the wall is an observer at rest.
$∴$ Frequency of sound reaching the wall is
$f^{'} = \frac{v f}{v - v_{s}} (1)$
where $v$ is the velocity of sound in air and $v_{s}$ is velocity of source.
On reflection, the wall is the source of sound of frequency $f^{'}$ at rest and bat is an observer approaching the wall with speed
$v_{0} = v_{s} = 4 m s^{- 1}$
$∴$ Frequency heard by the bat is
$f^{''} = \frac{f^{'} (v + v_{0})}{v} = f (\frac{v + v_{0}}{v - v_{s}}) [Using (1)]$
$90 \times 10^{3} (\frac{330 + 4}{330 - 4}) = \frac{90 \times 10^{3} \times 334}{326}$
$\approx 92.2 \times 10^{3} H z .$

KCET - 2010

PHXI15:WAVES

354695 The driver of a car travelling with speed $30 m s^{- 1}$ towards a hill sounds a horn of frequency $600 H z$ . If the velocity of sound in air is $330 m s^{- 1}$ , the frequency of reflected sound as heard by driver is

1

550 H z

2

555.5 H z

3

720 H z

4

500 H z

Explanation:

When the sound is reflected from the cliff, it approaches the driver of the car. Therefore, the driver acts as an observer and both sources (car) and observer are moving.
In this case, the apparent frequency heard by the driver (observer),
$f^{'} = f (\frac{v + v_{0}}{v - v_{0}})$
Given, $f = 600 H z, v = 330 m s^{- 1}, v_{0} = 30 m s^{- 1}$
$f^{'} = 600 (\frac{330 + 30}{330 - 30}) = 720 H z$

AIIMS - 2017

PHXI15:WAVES

354696 A tuning fork of frequency $380 H z$ is moving towards a wall with a velocity of $4 m / s$ . Then the number of beats heard by a stationary listener between direct and reflected sounds will be:(velocity of sound in air is $340 m / s$ )
supporting img

1

5

2

0

3

10

4

7

PHXI15:WAVES

354697 A motor car blowing a horn of frequency $124 H z$ moves with a velocity $72 k m / h r$ towards a tall wall. The frequency of the refelected sound heard by the driver will be (velocity of sound in air is $330 m / s)$

1

132 H z

2

109 H z

3

248 H z

4

140 H z

Explanation:

The frequency of reflected sound heard by the driver
The frequency received by the wall is
$f_{1} = f (\frac{v}{v - v_{s}})$
The frequency received by the car from wall is
$f_{2} = f_{1} (\frac{v + v_{s}}{v}) \Rightarrow f_{2} = f (\frac{v + v_{s}}{v - v_{s}})$
$= 124 [\frac{330 + (72 \times 5 / 18)}{330 - (72 \times 5 / 18)}] = 140 H z$

PHXI15:WAVES

354693 A toy-car, blowing its horn, is moving with a steady speed of $5 m / s$ , away from a wall. An observer, towards whom the toy car is moving, is able to hear 5 beats per second. If the velocity of sound in air is $340 m / s$ , the frequency of the horn of the toy car is close to :

1

680 H z

2

510 H z

3

340 H z

4

170 H z

Explanation:

From Doppler's effect
$f (direct) = f (\frac{340}{340 - 5}) = f_{1}$
Frequency received the wall $= \frac{340}{340 + 5}$
Frequency received by the person from the wall is $f ($ from wall $) = f (\frac{340}{340 + 5}) = f_{2}$
Beats $= (f_{1} - f_{2})$
$5 = f (\frac{340}{340 - 5} - \frac{340}{340 + 5})$
$\Rightarrow f = 170 H z$

JEE - 2016

PHXI15:WAVES

354694 A bat flies at a steady speed of $4 m s^{- 1}$ emitting a sound of $f = 90 \times 10^{3}$ . It is flying horizon tally towards a vertical wall. The frequency of the reflected sound as detected by the bat will be (Take velocity of sound in air as $330 m s^{- 1}$ )

1

88.1 \times 10^{3} H z

2

87.1 \times 10^{3} H z

3

92.2 \times 10^{3} H z

4

89.1 \times 10^{3} H z

Explanation:

Here, the bat is a source of sound and the wall is an observer at rest.
$∴$ Frequency of sound reaching the wall is
$f^{'} = \frac{v f}{v - v_{s}} (1)$
where $v$ is the velocity of sound in air and $v_{s}$ is velocity of source.
On reflection, the wall is the source of sound of frequency $f^{'}$ at rest and bat is an observer approaching the wall with speed
$v_{0} = v_{s} = 4 m s^{- 1}$
$∴$ Frequency heard by the bat is
$f^{''} = \frac{f^{'} (v + v_{0})}{v} = f (\frac{v + v_{0}}{v - v_{s}}) [Using (1)]$
$90 \times 10^{3} (\frac{330 + 4}{330 - 4}) = \frac{90 \times 10^{3} \times 334}{326}$
$\approx 92.2 \times 10^{3} H z .$

KCET - 2010

PHXI15:WAVES

354695 The driver of a car travelling with speed $30 m s^{- 1}$ towards a hill sounds a horn of frequency $600 H z$ . If the velocity of sound in air is $330 m s^{- 1}$ , the frequency of reflected sound as heard by driver is

1

550 H z

2

555.5 H z

3

720 H z

4

500 H z

Explanation:

When the sound is reflected from the cliff, it approaches the driver of the car. Therefore, the driver acts as an observer and both sources (car) and observer are moving.
In this case, the apparent frequency heard by the driver (observer),
$f^{'} = f (\frac{v + v_{0}}{v - v_{0}})$
Given, $f = 600 H z, v = 330 m s^{- 1}, v_{0} = 30 m s^{- 1}$
$f^{'} = 600 (\frac{330 + 30}{330 - 30}) = 720 H z$

AIIMS - 2017

PHXI15:WAVES

354696 A tuning fork of frequency $380 H z$ is moving towards a wall with a velocity of $4 m / s$ . Then the number of beats heard by a stationary listener between direct and reflected sounds will be:(velocity of sound in air is $340 m / s$ )
supporting img

1

5

2

0

3

10

4

7

PHXI15:WAVES

354697 A motor car blowing a horn of frequency $124 H z$ moves with a velocity $72 k m / h r$ towards a tall wall. The frequency of the refelected sound heard by the driver will be (velocity of sound in air is $330 m / s)$

1

132 H z

2

109 H z

3

248 H z

4

140 H z

Explanation:

The frequency of reflected sound heard by the driver
The frequency received by the wall is
$f_{1} = f (\frac{v}{v - v_{s}})$
The frequency received by the car from wall is
$f_{2} = f_{1} (\frac{v + v_{s}}{v}) \Rightarrow f_{2} = f (\frac{v + v_{s}}{v - v_{s}})$
$= 124 [\frac{330 + (72 \times 5 / 18)}{330 - (72 \times 5 / 18)}] = 140 H z$

Explanation:

Explanation:

Explanation:

Explanation:

Explanation:

Explanation:

Explanation:

Explanation:

Explanation:

Explanation:

Explanation:

Explanation:

Explanation:

Explanation:

Explanation:

Question Bank Series

Explanation:

Explanation:

Explanation:

Explanation:

Explanation:

Explanation:

Explanation:

Explanation:

Explanation:

Explanation: