Tag: physics

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

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

  1. lesser

  2. larger

  3. same

  4. may be lesser or may be larger
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Force $= mass\times acceleration$

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

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

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 :

  1. the principle of rocket propulsion

  2. the principle of combustion

  3. the principle of conservation of energy

  4. None of the above
Reveal answer Fill a bubble to check yourself
A Correct answer
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.

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

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

  1. PAYBOOK

  2. PLAYOAD

  3. PAYLOAD

  4. PLAYWOOD
Reveal answer Fill a bubble to check yourself
C Correct answer
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.

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

The principle of rocket propulsion depends on :

  1. Newton's third law of motion

  2. Principle of conservation of momentum

  3. Either A and B

  4. Both A and B
Reveal answer Fill a bubble to check yourself
D Correct answer
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.

Multiple choice physics superposition and interference of sound waves

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

  1. $I = 100\ I _{0}$
  2. $I = 10\ I _{0}$
  3. $I = I _{0}$
  4. $I = \surd {10}\ I _{0}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

For incoherent sources (random phases), the intensities add linearly. If there are 10 sources each with intensity I0, the total intensity is 10 * I0.

Multiple choice physics superposition and interference of sound waves

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 $350m/sec$)

  1. $0.7mm$
  2. $0.1mm$
  3. $0.2mm$
  4. $0.5mm$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

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

Multiple choice physics superposition and interference of sound waves

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?

  1. $8$
  2. $6$
  3. $4$
  4. $3$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The beat frequency is the difference between the two frequencies. f1 = 100/2 = 50 Hz, f2 = 92/2 = 46 Hz. Beat frequency = 50 - 46 = 4 Hz.

Multiple choice physics superposition and interference of sound waves

 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: 

  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 $
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The resultant amplitude of two waves with amplitude A and phase difference phi is sqrt(A^2 + A^2 + 2*A*A*cos(phi)). For phi = pi/2, this is sqrt(2*A^2) = A*sqrt(2). The frequency remains the same.

Multiple choice physics superposition and interference of sound waves

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

  1. 4 : 1

  2. 9 : 1

  3. 2 : 1

  4. 10 : 8
Reveal answer Fill a bubble to check yourself
A Correct answer
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       $\dfrac{I _{max}}{I _{min}}  =  \dfrac{(\sqrt{I _1} + \sqrt{I _2})^2}{(\sqrt{I _2} - \sqrt{I _1})^2} = \dfrac{(\sqrt{I _1} + \sqrt{9  I _1})^2}{(\sqrt{9  I _1} - \sqrt{I _1})^2} = \dfrac{16  I _1}{4  I _1}$ 

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