Tag: physics

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Questions Related to physics

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

A laser signal sent towards the moon returns after T seconds.If c is the speed of light, then  the distance of the moon from the observer is given by

  1. cT
  2. $c{T^{ - 2}}$
  3. $\frac{{ct}}{2}$

  4. 2 cT
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The total distance traveled by the signal is 2 * distance (to and back). Since distance = speed * time, 2 * d = c * T, therefore d = c * T / 2.

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 is $330 ms^{-1}$ and that of light is $3\times 10^8 ms^{-1}$. The ratio of speed of sound to that of light is approximately $1 : 10^6$.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Speed Of Sound$(V)$  is,  $330m/s$  and  that of Light$(U)$  is,  $300*10^{6}m/s$

Now we have to find,  $V:U$  and i.e.,  $V:U=330:300*10^{6}\cong1:10^{6}$ , because in comparison to $U$(Speed of Light)  ,  Speed of Sound$(V)$  is comparetively very $small$.
So, we can assume that, Speed of Sound$(V)$  is $300m/s$  in comparison to that of Speed of Light$(U)$ that is  $3*10^{6}$
Hence,  $V:U=1:10^{6}$

Hence, it is True.
Option A 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

If you hear a gun shot 1 seconds after it is fired, how far away from the gun are you? (speed of sound in air $=330 ms^{-1})$

  1. 230 m

  2. 330 m

  3. 430 m

  4. 530 m
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Here we use the concept of Distance formula i.e.,  $d=vt$ , where  $d$  is the distance travelled,  $v$  is the speed and $t$  is the time taken.

Now, According to question;
Given;  $t=1s$  and  $v=330m/s$,
have to find  $d$  and that is,  $d=vt=330*1=330m$

Hence, option  B  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

Light .......... travel in vacuum , but the sound ........ travel in vacuum.

  1. Cannot , can

  2. Can, cannot

  3. Sometimes, never

  4. Never, sometimes
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The light can travel in vacuum, but the sound can not travel in vacuum. speed of light in air is $\displaystyle 3\times { 10 }^{ 8 }{ m }/{ s }$

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

Speed of light in air is about ....... times greater than the speed of sound in air.

  1. Million

  2. Trillion

  3. Billion

  4. None
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The speed of light in air is $\displaystyle 3\times { 10 }^{ 8 }{ m }/{ s }$ which is about a million times greater than the speed of sound in air (i.e. 330 m/s at $\displaystyle { 0 }^{ \circ  }C$

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 ,
        $T=t+t'=10+1.47=11.47s$