Tag: comparison of speed of sound with speed of light

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Multiple choice physics propagation of sound waves longitudinal vs transverse wave sound and light comparison of speed of sound with speed of light

An aeroplane travelling at the speed of sound will have a velocity of:

  1. 1000 km/hr

  2. 1180 km/hr

  3. 1540 k/hr

  4. 1620 k/hr
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Speed of sound in air is , $v=330m/s=330\times18/5=1188km/hr$ , as stated that aeroplane is travelling with the velocity of sound therefore its velocity is $1188km/hr$ .

Multiple choice physics propagation of sound waves longitudinal vs transverse wave sound and light comparison of speed of sound with speed of light

The correct statement is:

  1. Sound and light both require medium for propagation.

  2. Sound can travel in vacuum, but light can not.

  3. Sound needs medium, but light does not need medium for its propagation.

  4. Sound and light both can travel in vacuum.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Sound waves need to travel through a medium such as a solid, liquid, or gas. The sound waves move through each of these mediums by vibrating the molecules in the matter. The molecules in solids are packed very tightly. Liquids are not packed as tightly as solids. And gasses are very loosely packed. The spacing of the molecules enables sound to travel much faster through a solid than a gas. Sound travels about four times faster and farther in water than it does in air. 
Sound waves are traveling vibrations of particles in media such as air, water or metal. So it stands to reason that they cannot travel through empty space, where there are no atoms or molecules to vibrate.
Light travels as a wave. But unlike sound waves or water waves, it does not need any matter or material to carry its energy along. This means that light can travel through a vacuum, a completely airless space. Nothing travels faster than light energy. 
Hence, the statement "Sound needs medium, but light does not need medium for its propagation." is correct.

Multiple choice physics propagation of sound waves longitudinal vs transverse wave sound and light comparison of speed of sound with speed of light

 A stone is dropped from the top of a tower $500$m high into a pond of water at the base of the tower. When is the splash heard at the top ? (Given $g = 10 ms^{-2}$ and speed of sound =$ 340 ms^{-1}$)

  1. $10s$

  2. $11.47s$

  3. $1.10s$

  4. $20s$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Given -  $h=500m   ,  g10m/s^{2} ,  v=340m/s$ ,

by ,  $h=ut+(1/2)gt^{2}$ ,
        $500=0+(1/2)10t^{2}$  ,   (initial velocity , $u=0$) ,
or     $t^{2}=1000/10=100$ ,
or     $t=10s$ ,
it is the time taken by stone to reach the water level , after that a sound is produced due to strike of stone on water , and sound travels upwards .Let t' be the time taken by sound to reach the base of tower ,
then , $t'=h/v=500/340=1.47s$ ,
therefore time taken by splash to hear at the top ,
        $T=t+t'=10+1.47=11.47s$

Multiple choice physics propagation of sound waves longitudinal vs transverse wave sound and light comparison of speed of sound with speed of light

The sound of lightning flash is heard $3$ second after the flash is seen. The distance of the lightning is $1020$ metre. The speed of sound is:

  1. $1400\ m/s$

  2. $332\ m/s$

  3. $340\ m/s$

  4. $none\ of\ these$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Given data,
Distance $d=1020 m$
Time $t=3s$
Speed$=?$
$Speed=\dfrac{distance }{time}=\dfrac{1020}{3}=340 m/s$

Multiple choice physics propagation of sound waves longitudinal vs transverse wave sound and light comparison of speed of sound with speed of light

The speed of sound in air is  330m/s. It takes 10s for sound to reach a certain distance from the source placed in air. Find the distance.

  1. 669m

  2. 330m

  3. 3300m

  4. 1200m
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

$\displaystyle V=330{ m }/{ s },t=2s,V=\frac { d }{ t } $
$\displaystyle d=V\times t$
$\displaystyle =330\times 10=3300m$

Multiple choice physics propagation of sound waves longitudinal vs transverse wave sound and light comparison of speed of sound with speed of light

The smoke from a gun barrel is seen 10s before the explosion is heard. If the speed of sound in air is 340 m/s. Calculate the distance of observer from the gun :

  1. 3400m

  2. 2402m

  3. 62m

  4. 900m
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Speed of sound = 340 m/s
time = 10s
Speed = Distance travelled / time taken
Distance = speed x time
=340 x 10 = 3400 m.

Multiple choice physics propagation of sound waves longitudinal vs transverse wave sound and light comparison of speed of sound with speed of light

On a hot, dry summer day a boy is standing between plane parallel vertical cliffs separated by $75m$. He is $30$m away from one of the cliffs. Consider speed of sound in air on that hot day to be $360m/s$. The boy claps loudly and hearts its successive echoes. The time in seconds at which he hears the first four echoes are respectively

  1. $\displaystyle \frac{1}{6}, \frac{1}{4}, \frac{5}{12}, \frac{5}{12}$

  2. $\displaystyle \frac{1}{6}, \frac{1}{4}, \frac{7}{12}, \frac{2}{3}$

  3. $\displaystyle \frac{1}{4}, \frac{1}{3}, \frac{5}{12}, \frac{5}{12}$

  4. $\displaystyle \frac{1}{6}, \frac{1}{4}, \frac{1}{3}, \frac{5}{12}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

First echo : When sound goes to the cliff 1 and returns to his ear

Distance traveled by sound, $S = 30+30 = 60$ m
Time taken, $t _1 = \dfrac{60}{360} = \dfrac{1}{6}$ s

Second echo : When sound goes to the cliff 2 and returns to his ear
Distance traveled by sound, $S = 45+45 = 90$ m
Time taken, $t _2 = \dfrac{90}{360} = \dfrac{1}{4}$ s

Third echo : When the reflected sound from cliff 1 goes to the cliff 2 and returns to his ear
Distance traveled by sound, $S = 30+75+45 = 150$ m
Time taken, $t _3 = \dfrac{150}{360} = \dfrac{5}{12}$ s

Fourth echo : When the reflected sound from cliff 2 goes to the cliff 1 and returns to his ear
Distance traveled by sound, $S = 45+75+30 = 150$ m
Time taken, $t _4 = \dfrac{150}{360} = \dfrac{5}{12}$ s