Physics · Science General

Escape Velocity and Rockets

92 Questions

Escape velocity and rockets questions cover spacecraft trajectories and gravitational influences. The topics include calculating maximum velocities and understanding multistage rocket mechanics. These physics concepts are essential for technical exams requiring scientific aptitude.

Escape velocityOrbital mechanicsRocket propulsionAtmospheric entry speedsGravitational pull

Escape Velocity and Rockets Questions

Multiple choice

During a journey from Earth to Moon and back, the greatest energy required from the spaceship's rocket is to overcome

  1. Earth's gravity during take-off

  2. the moon's gravity at lunar landing

  3. the moon's gravity during take-off

  4. Earth's gravity when entering into the atmosphere

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

Earth's gravity is strongest at the surface (9.8 m/s²) and requires enormous energy to overcome during takeoff. The rocket must achieve ~11.2 km/s (escape velocity) to break free. Moon's gravity is only 1/6th of Earth's and requires much less energy. Re-entry uses atmospheric drag, not rocket power.

Multiple choice

When a rocket moves in space in a straight line with a constant speed, it is far from the gravitational effect of any star or planet. Which of the following forces must be applied to the rocket to sustain its motion?

  1. Force equal to the weight of the rocket

  2. Force equal to the mass of the rocket

  3. Force equal to the speed of the rocket

  4. No external force is required

  5. Force equal and opposite to the gravity of the earth
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

  

Multiple choice

Escape velocity from the earth's surface is

  1. equal to that from the moon's surface

  2. greater than that from the moon's surface

  3. less than that from the moon's surface

  4. equal to that from the sun's surface
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Escape velocity depends on mass and radius: v = √(2GM/R). Earth's higher mass-to-radius ratio gives it an escape velocity of about 11.2 km/s, while the Moon's is only about 2.4 km/s. The Moon's lower gravity means less speed is needed to overcome it.

Multiple choice

The escape velocity of an object from the surface of the earth is 11.6km/s. if the mass of the earth is increased four times, the resultant escape velocity would be-

  1. (11.6*1/2) km/s

  2. 11.6 km/s

  3. (11.2*2 km/s)

  4. (11.6*4 km/s)
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Escape velocity is calculated using the formula v = sqrt(2GM/R). If the mass (M) of the Earth increases four times while the radius (R) remains constant, the new escape velocity becomes sqrt(4) times the original, which is 2 times the original velocity. Although the question uses 11.6 km/s as a base, the standard value is 11.2 km/s, and the correct logic is doubling that value.

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

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

  1. $11.2 \ kms^{-1}$
  2. $11 \ kms^{-1}$
  3. $22 \ kms^{-1}$
  4. $22.2 \ kms^{-1}$
Reveal answer Fill a bubble to check yourself
A Correct answer
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  $v _{e}=\sqrt{2\times9.8\times6.4\times10^{3}}=11.2kms^{-1}$

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

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

  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$
Reveal answer Fill a bubble to check yourself
B Correct answer
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        $v _{e}=\sqrt2v _{o}$ 

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

Payload ratio is :

  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
Reveal answer Fill a bubble to check yourself
B Correct answer
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. 

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

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

  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
Reveal answer Fill a bubble to check yourself
D Correct answer
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.

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

Multistage rocket is used because:

  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
Reveal answer Fill a bubble to check yourself
A Correct answer
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.

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

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.

  1. A, B and C

  2. Only B and C

  3. Only C

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

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.