Tag: physics

Questions Related to physics

Fill in the blank.
Larger the mass of the  rocket _____ is the acceleration.

physics satellite launch vehicles rocket propellants universe and space science xx radio telescope and space telescopes launching vehicles

  1. lesser

  2. larger

  3. same

  4. may be lesser or may be larger

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Correct Option: A
Explanation:

Force $= mass\times acceleration$

Since force depends on the engine and the fuel, force is constant.
Greater the mass, lesser is the acceleration.

Blow a balloon and let it go. You will find it moving in the direction opposite to the direction in which the air is ejected. This demonstrates :

physics satellite launch vehicles rocket propellants universe and space science xx radio telescope and space telescopes launching vehicles

  1. the principle of rocket propulsion

  2. the principle of combustion

  3. the principle of conservation of energy

  4. None of the above

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Correct Option: A
Explanation:

The principle of rocket propulsion works on the 'Newton's Third Law of Motion'. It states that, 'to every action, there is always an equal and opposite reaction'.

In the case of a rocket, the engine emits hot burning gases in the downward direction. These gases apply an equal and opposite reaction force to the rocket in the upward direction.
This is how a rocket is propelled.
Rocket propulsion is similar to the example of the situation in which, if we blow a balloon and let it go, it starts moving in the direction opposite to the direction in which the air is ejected. 
Balloon forces out the air inside it. The air applies an equal and opposite reaction force to the balloon.

The scientific instrument which is usually placed in the front region of the rocket is called :

physics satellite launch vehicles rocket propellants universe and space science xx radio telescope and space telescopes launching vehicles

  1. PAYBOOK

  2. PLAYOAD

  3. PAYLOAD

  4. PLAYWOOD

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Correct Option: C
Explanation:

The scientific instrument placed in the front region of the rocket is called PAYLOAD. For a rocket payload can be a satellite, space probe or a space craft carrying humans. The fraction of payload to the total liftoff weight of the rocket iscalled as palyload friction.

The principle of rocket propulsion depends on :

physics satellite launch vehicles rocket propellants universe and space science xx radio telescope and space telescopes launching vehicles

  1. Newton's third law of motion

  2. Principle of conservation of momentum

  3. Either A and B

  4. Both A and B

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Correct Option: D
Explanation:

The principle of rocket propulsion works on the 'Newton's Third Law of Motion'. It states that, 'to every action, there is always an equal and opposite reaction'.

In the case of a rocket, the engine emits hot burning gases in the downward direction. These gases apply an equal and opposite reaction force to the rocket in the upward direction.
This is how a rocket is propelled.
The principle of conservation of momentum states that whenever two bodies collide or get separated, then their  total momentum before collision or separation is equal to their total momentum after collision or separation.
Since the gases of the rocket and the rocket are stationery at the start, their total momentum is zero. After the gases start burning, the momentum imparted to the rocket is equal and opposite to that of the gases. Hence their total momentum is zero.

Four sources of sound each of sound level 10 dB are sounded together in phase, the resultant intensity level will be ($log _{10}2 = 0.3$)

physics superposition and interference of sound waves

  1. 40 dB

  2. 26 dB

  3. 22 dB

  4. 13 dB

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Correct Option: D

Consider ten identical sources of sound all giving the same frequency but having phase angles which are random. If the average intensity of each source is $I _{0}$, the average of resultant intensity $I$ due to all these ten sources will be

physics superposition and interference of sound waves

  1. $I = 100\ I _{0}$

  2. $I = 10\ I _{0}$

  3. $I = I _{0}$

  4. $I = \surd {10}\ I _{0}$

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Correct Option: B

Two sources of sound A and B produce the wave of $350Hz$, they vibrate in the same phase. The particle $P$ is vibrating under the influence of these two waves. If the amplitude at the point $P$ produced by the two waves is $0.3mm$ and $0.4mm$ then the resultant amplitude of the point $P$ will be: (path difference $AP-BP=25cm$ and the velocity of sound is $350m/sec$)

physics superposition and interference of sound waves

  1. $0.7mm$

  2. $0.1mm$

  3. $0.2mm$

  4. $0.5mm$

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Correct Option: D
Explanation:

$\begin{array}{l} \lambda =\dfrac { v }{ n } =\dfrac { { 350 } }{ { 350 } } =1m=100cm \ Path\, difference\, \, \Delta x=AP-BP=25cm \ Phase\, difference\, \, \Delta \varphi =\dfrac { { 2\pi  } }{ \lambda  } \Delta x=\dfrac { { 2\pi  } }{ 1 } \times \left( { \dfrac { { 25 } }{ { 100 } }  } \right) =\dfrac { \pi  }{ 2 }  \ Amplitude\, A=\sqrt { { { \left( { { a _{ 1 } } } \right)  }^{ 2 } }+{ { \left( { { a _{ 2 } } } \right)  }^{ 2 } } } =\sqrt { { { \left( { 0.3 } \right)  }^{ 2 } }+{ { \left( { 0.4 } \right)  }^{ 2 } } } =0.5mm \end{array}$

Two plane harmonic sound waves travelling in the same direction are given by the following displacement equations
$y _{1} (x, t) = A\cos (0.5\pi x - 100\pi t)$
$y _{2} (x, 1) = A\cos (0.46\pi x - 92\pi t)$
How may times, a listener can hear sound of maximum intensity in one second?

physics superposition and interference of sound waves

  1. $8$

  2. $6$

  3. $4$

  4. $3$

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Correct Option: C

 When two sound waves with a phase of $\dfrac { \pi  }{ 2 } $ and each having amplitude A and frequency $\omega $, are superimposed on each other, then the maximum amplitude and frequency  of resultant wave is: 

physics superposition and interference of sound waves

  1. $\sqrt { 2 } A;\omega $

  2. $\dfrac { A }{ \sqrt { 2 } } ;\dfrac { \omega }{ 2 } $

  3. $\left( \sqrt { 2 } \right) A;\dfrac { \omega }{ 2 } $

  4. $\dfrac { A }{ \sqrt { 2 } } ;\omega $

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Correct Option: A

Two waves having the intensities in the ratio 9 : 1 produce interference. The ratio of maximum to minimum intensity is equal to

physics superposition and interference of sound waves

  1. 4 : 1

  2. 9 : 1

  3. 2 : 1

  4. 10 : 8

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Correct Option: A
Explanation:

Let the intensity of the two waves be $I _1$  and  $I _2$


Given:    $I _2  :  I _1  =  9  :  1        \implies  I _2   =  9  I _1$

Now       $\dfrac{I _{max}}{I _{min}}  =  \dfrac{(\sqrt{I _1} + \sqrt{I _2})^2}{(\sqrt{I _2} - \sqrt{I _1})^2} = \dfrac{(\sqrt{I _1} + \sqrt{9  I _1})^2}{(\sqrt{9  I _1} - \sqrt{I _1})^2} = \dfrac{16  I _1}{4  I _1}$ 

$\implies    I _{max}  :  I _{min}  =  4  : 1$