Tag: rocket propellants

Questions Related to rocket propellants

The formula for critical velocity is :

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  1. $\sqrt {2R g}$

  2. $\dfrac{R}{g}$

  3. $\dfrac{3R}{2g}$

  4. $\sqrt {R g}$

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Correct Option: D
Explanation:

The velocity required to put a satellite in its orbit around a planet is called critical velocity .The critical velocity or orbital velocity of a satellite of planet of radius $R$ is given by $v _{o}=\sqrt{gR}$ 

The escape velocity for any satellite to be placed in a orbit is :

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  1. $11.2 \ kms^{-1}$

  2. $11 \ kms^{-1}$

  3. $22 \ kms^{-1}$

  4. $22.2 \ kms^{-1}$

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Correct Option: A
Explanation:

The escape velocity on a  planet of radius $R$ is given by  ,

           $v _{e}=\sqrt{2gR}$  
for earth -  $R=6.4\times10^{3}km , g=9.8m/s^{2}$
hence  $v _{e}=\sqrt{2\times9.8\times6.4\times10^{3}}=11.2kms^{-1}$

The correct relation between escape velocity $v _e$ and critical velocity $v _0$ is :

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  1. $ v _e=\sqrt{\dfrac{3}{2}} v _0$

  2. $ v _e=\sqrt{2} v _0$

  3. $ v _e=\sqrt{3}v _0$

  4. $ v _e=\sqrt{\dfrac{2}{3}}v _0$

Show answer
Correct Option: B
Explanation:

The critical velocity or orbital velocity of a satellite of planet of radius $R$  is given by  ,

           $v _{o}=\sqrt{gR}$  ..................eq1
The escape velocity on a  planet of radius $R$ is given by  ,
           $v _{e}=\sqrt{2gR}$  ..................eq2
dividing eq2 by eq1 , we get
           $\dfrac{v _{e}}{v _{o}}=\dfrac{\sqrt{2gR}}{\sqrt{gR}}=\sqrt2$ 
or        $v _{e}=\sqrt2v _{o}$ 

Payload ratio is :

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  1. $\dfrac{\text{fuel mass}}{\text{payload mass}}$

  2. $\dfrac{\text{payload mass}}{\text{fuel mass}}$

  3. $\dfrac{\text{payload mass}}{\text{total rocket mass}}$

  4. None of the above

Show answer
Correct Option: B
Explanation:

Payload ratio is the ratio of mass that a payload carries and take-off weight. Take-off weight in case of short trips is almost equal to fuel mass. 

Which of the following satellites have been successfully built by India ?

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  1. Communication Satellites

  2. Meteorological Satellites

  3. Remote Sensing Satellites

  4. All of the above

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Correct Option: D
Explanation:

All the given satellites have successfully built .

Communication satellite-GSAT-18
Meteorological satellite- INSAT-3D
Remote Sensing satellite- Bhaskara-1

When the fuel in the rocket burns, the rocket moves vertically upward due to :

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  1. the exhaust gases escape through the nozzle opposite to the earth and pushes downwards

  2. the exhaust gases escape through the nozzle opposite to the earth and pushes upwards

  3. the exhaust gases escape through the nozzle towards the earth and pushes downwards

  4. the exhaust gases escape through the nozzle towards the earth and pushes upwards

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Correct Option: D
Explanation:

We know that by newton's third law of motion, Every action has an equal and opposite reaction. So as the fuel burns it escapes from the nozzle towards the earth. So the gases exert an equal and opposite force on the rocket. So this propels the rocket vertically upward.

Multistage rocket is used because:

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  1. a single rocket  cannot push satellite to a great height

  2. a single rocket cannot carry huge amount of fuel

  3. the speed of a single rocket is less

  4. none of the above

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Correct Option: A
Explanation:

A multi-stage rocket consists of several pieces of fuel containers joined in series. Whenever any container's fuel starts burning, obviously the fuel quantity starts decreasing. When the container is completely empty, it is detached from the rocket and the second container starts working. This reduces the mass and weight of the rocket, enabling it to travel faster than before. After the 2nd gets empty, that is also detached and the third starts working, and so on. Thus there is rapid gain in speed continuously.


In a single stage rocket, there is only one large container which contains all the fuel. It cannot be detached from the rocket. Its speed doesn't increase as rapidly as a multi-stage one.

A multi-stage rocket can launch a satellite to a much greater height as compared to a single-stage one.

Streamlining of the rocket :

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  1. minimizes the friction of air.

  2. maximizes the friction of air.

  3. Either A or B is correct depending on the weight of the rocket.

  4. Both A and B.

Show answer
Correct Option: A
Explanation:

Whenever any object moves through air, air opposes the motion. This is known as air resistance. 

The intensity of air resistance depends on the area of the surface which is perpendicular to the direction of motion.
To reduce this resistance, the face of the rocket is made almost conical. This is known as streamlining. 
Streamlining minimizes air resistance and increases the speed of the rocket. 

Which of the following need to be considered when the rocket operates:
(A): As the rocket consumes fuel at every instant, its mass goes on decreasing.
(B): The acceleration due to gravity changes continuously as the rocket ascends.
(C): The atmosphere offers resistance in the lower strata of atmosphere.

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  1. A, B and C

  2. Only B and C

  3. Only C

  4. None of the above

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Correct Option: A
Explanation:

As the rocket consumes fuel at every instant, the fuel is converted to gases and are thrown out of the rocket. Hence the fuel content gets lesser and lesser as the fuel burns. Thus the mass goes on decreasing.

When these gases are thrown out, they exert a force on the rocket and it gets propelled.
As per the equation, $force = {mass}\times{acceleration}$, lesser the mass, greater is the acceleration of the rocket. This point must be considered while studying the motion of the rocket.
The acceleration due to gravity changes continuously as the rocket ascends because, the downward gravitational force acting on any object becomes lesser and lesser as it goes away from the earth. Hence the net force acting on the rocket goes on increasing.
This point must also be considered
In the lower strata of atmosphere, its density is more. Hence it offers greater resistance to moving bodies. The rocket has to thus overcome this force of resistance at lower height. This decreases the net force acting on the rocket at lower height.

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

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  1. lesser

  2. larger

  3. same

  4. may be lesser or may be larger

Show answer
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.