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Given, 

Time for echo = 0.8 sec 

Height of building = 132.8 m 

Distance travelled by sound = 2×height 

Distance travelled = 2×132.8 = 265.6 m

Speed of Sound = \(\frac{distance}{time}\) = \(\frac{265.6}{0.8}\) = 332ms^-1

Velocity = 2D/Time

3 × 10⁸ = 2 x 45 x 1000/ Time

Time = 90000/ 3 × 10⁸ = 3 × 10^-4 second

2 D = velocity × time

D = (velocity × time) / 2 = 1450 × 4 / 2 = 2900 m = 2.9 km

Velocity = 2 × D/Time

Time after which an echo is heard = 2 D/Velocity = 2 × 48 / 320 = 0.3 seconds

Speed of sound = 310ms^-1 

time after which echo is heard t = 1.5s distance from cliff d = ? 

2d = Speed × t

d=300 t = ? v = 3 × 10⁸ms^-1 

t=2d/v = 2 × 300 × 1000m/3 ×10⁸ ms^-1 

= 0.002 s = 2 × 10^-3s

A sound persists in our ear for 0.1 s. At temperature 22℃ in air and speed of sound 344 ms^-1, the total distance covered by sound between the point of generation and reflecting surface should be at least (344 m/s) x 0.1 s = 34.4 m. Thus, the minimum distance between the point of generation and reflecting surface should be half of it i.e. 17.2 m. So, we cannot hear the echo in a smaller room of 10 m.

Correct option is: (B) 17.2

Transmission of sound occurs at a different speed through different mediums. Transmission of sound is faster through a solid than through a liquid and gas.

The answer is (A) frequency

(a) 50,000Hz can be heard by dog but not human being.

The answer is (D) decreased by a factor of 4

No, sound cannot travel through vacuum.

Sound is a mechanical wave and requires a medium to propagate. As the moon has no atmosphere, it has an absence of air. So, there is no medium for sound to propagate. So, two astronauts cannot hear each other on the moon.

Astronauts use radio waves for communications.

The answer is (B) Below 20 Hz

Two astronauts on the moon talking to each other directly, will be unable to listen to each other, even if they are very close to each other. The moon does not have atmosphere. Since there is no medium which is necessary for generation and propagation of sound, between the astronauts, direct sound propagation between them is not possible. Therefore, the astronauts use some technology like the one used in our cell-phones to communicate with each other. The waves used in cell-phone do not need any medium for propagation.

The answer is (A) 0.1 S

The answer is (B) Rarefaction

Propagation of sound through air occurs due to energy transfer by vibrating air molecules in one region to those in the adjacent region away from the source. The molecules simply vibrate about their mean positions. Hence, the air itself is not required to move from one place to the other.

Sound produced by a vibrating body travels to our ears by the actual movement of air False. 

Soufid travels in the form of waves. It reaches our ears from the source of its production, in the form of waves.

No, we must never put a pin or pencil in our ears, because it can tear our ear diaphragm.

True In a longitudinal wave, compression and rarefaction are formed.

Crest: It is the highest point the medium rises to while the propagation of waves.

Trough: It is the lowest point a medium fall to while the propagation of the wave.

Transverse wave: In a transverse wave, particles oscillate up and down about their mean position in a direction perpendicular to the direction of propagation of wave. e.g. light waves 

Longitudinal wave: In a longitudinal wave, the individual particles of the medium move in a direction parallel to the direction of propagation of the wave. The particles oscillate back and forth about their position of rest. e.g. Sound wave

The correct answer is c) slinky

Sound waves in air: longitudinal, compression, rarefaction Water waves: transverse, crest, trough

False 

Explanation: 

Sound waves are longitudinal waves. They propagate when the particles of the medium oscillate back and forth about their position of rest and do not move from one place to another. 

Light waves are transverse waves but the particles in oscillation are not of the medium as it is not a mechanical wave. 

a) Mass number of X = 16 (∵ number protons + number neutrons) 

b) Mass number of Y = 17 

c) Isotopes 

d) Oxygen ( \(^{16}_8O\) )

1. A sodium ion, Na⁺ has 10 electrons in it. 

2. Now, the maximum capacity of K shell is 2 electrons and that of L shell is 8 electrons. 

3. Taken together, the maximum capacity of K and L shells is 2 + 8 = 10 electrons. 

4. A sodium ion Na⁺ has completely filled K and L shells because its 10 electrons can completely fill up K and L shells.

Correct option is A) metre

Correct option is A) longitudinal

C) compressions

B) longitudinal

C) density, pressure

D) rarefactions

Correct option is B) wavelength

B) rarefaction

Correct option is A) wavelength

A) compression

Correct option is D) amplitude

Correct option is B) frequency

Frequency is expressed in Hertz.

The unwanted sound in our surroundings is called sound pollution.

Effects of sound pollution on biodiversity:

1. The first harmful effect is loss of hearing. 

2. It also leads to several health related problems, 

e.g : Sleeplessness, hypertension, increase in blood pressure, etc. 

3. It effects the mental health of people. 

4. In animals, noise can increase the risk of death by altering predator or prey detection and avoidance, interfere with reproduction and navigation and contribute to permanent hearing loss. 

5. Noise pollution causes poor quality of crops.

6. Under water animals such as whales and dolphins too experience discomfort due to noise pollution caused by submarines, shipping companies and sonars. Cuttle fish and octopus suffer serious damage from noise pollution.

The steps to reduce sound pollution : 

1. Attach silencers to the bikes and other machines to reduce sound. 

2. Manufacture machines that work with lesser noise. 

3. During the use of TVs and taperecorders tune down volume of sound.

4. Plant trees to reduce sound pollution.