Tag: gravitation: planets and satellites

Questions Related to gravitation: planets and satellites

The time period of a second's pendulum inside a satellite will be

physics gravitation: planets and satellites weightlessness application of newton's law of motion escape velocity

  1. zero

  2. $1$ sec

  3. $2$ sec

  4. infinite

Show answer
Correct Option: D
Explanation:

time period $\propto \sqrt { \cfrac { l }{ g }  } $ , as in the satellite there will be no gravity so the time period will be infinite.(logical explanation. : without gravity there will be no force on pendulum so it will not move a bit even in infinite time.)

In an earth satellite moving in a circular orbit, a piece of metal weighing $16g$ (on the earth) is weighed by a spring balance while the metal is suspended in water. If the relative density of the metal is $8$, what weight will be recorded?

physics gravitation: planets and satellites weightlessness application of newton's law of motion escape velocity

  1. $-2$ g

  2. zero

  3. $2$ g

  4. $14$ g

Show answer
Correct Option: B
Explanation:

In the satellite the spring is in free fall so no weight will be recorded.

The radius and mean density of the earth are $R$ & $p$ respectively . the critical orbital speed of a satellite for a low altitude orbit is 

physics gravitation: planets and satellites weightlessness application of newton's law of motion escape velocity

  1. $ 2 \sqrt {\dfrac { \pi G p}{3R}} $

  2. $ 2R \sqrt {\dfrac { \pi Gp}{3}} $

  3. $ 2R \sqrt {\dfrac {2 \pi G p}{3}} $

  4. $ 2R \sqrt {\dfrac { \pi Gp}{2}} $

Show answer
Correct Option: B

An astronaut, inside an earth satellite, experiences weightlessness because

physics gravitation: planets and satellites weightlessness application of newton's law of motion escape velocity

  1. no external force is acting on him

  2. he is falling freely

  3. no reaction is exerted by the floor of the satellite

  4. he is far away from the earth's surface

Show answer
Correct Option: B,C
Explanation:

For an earth satellite moving in a circular orbit, centripetal force required for its circular motion is provided by the gravitational force exerted by earth on it.
 It means resultant force on the astronaut is equal to the gravitational force exerted by earth on him. Hence, no reaction is exerted by floor of the satellite on him.
In other words, his acceleration towards earth centre (centripetal acceleration) is exactly equal to acceleration caused by the gravitational force alone.
Hence, options (b) and (c) are correct.

Weightlessness experienced while orbiting the earth in a spaceship is the result of

physics gravitation: planets and satellites weightlessness application of newton's law of motion escape velocity

  1. Inertia

  2. Accelaration

  3. Zero gravity

  4. Centre of gravity

Show answer
Correct Option: C
Explanation:

Weightlessness means that there is no reaction on a body from the floor. Since both the artificial satellite & the astronaut have same centripetal acceleration (as in a lift; which is falling freely, we does not feel any weight, because both lift & we fall with same acceleration). so the astronaut does not feel any weight inside the space craft

The period of a simple pendulum inside a satellite orbiting earth is

physics gravitation: planets and satellites weightlessness application of newton's law of motion escape velocity

  1. $\displaystyle zero$

  2. $\displaystyle \infty $

  3. can be any integer

  4. cant say

Show answer
Correct Option: B
Explanation:

$\displaystyle T=2\pi \sqrt {\frac{l}{g}}$
but inside the satellite $\displaystyle g=0$
So $\displaystyle T=\infty$ 

A body suspended from a spring balance is placed in a satellite. Reading in balance is $W _1$ when the satellite moves in an orbit of radius $R$. Reading in balance is $W _2$ when the satellite moves in an or bit of radius $2R.$ Then.

physics gravitation: planets and satellites weightlessness application of newton's law of motion escape velocity

  1. $W _1 = W _2$

  2. $W _1 > W _2$

  3. $W _1 < W _2$

  4. $W _1 =2 W _2$

Show answer
Correct Option: A
Explanation:

Since,Both the satellites are freely falling bodies.
so,$W _1=W _2$

Moon is a satellite of the Earth, but weightlessness is not experienced at the surface of the Moon because

physics gravitation: planets and satellites weightlessness application of newton's law of motion escape velocity

  1. its distance from the Earth is more.

  2. it is a natural satellite.

  3. its size is big but density is very low.

  4. its own mass is more.

Show answer
Correct Option: D
Explanation:

As Moon has its mass, thus it posses its own gravity ($\frac {1}{6}$th of that of the Earth). Hence, weightlessness is not experienced at the surface of the Moon.

Weightlessness experienced in a spaceship is due to

physics gravitation: planets and satellites weightlessness application of newton's law of motion escape velocity

  1. absence of of inertia.

  2. absence of gravity.

  3. absence of accelerating force.

  4. free fall of the spaceship.

Show answer
Correct Option: D
Explanation:

It is a misconception that there is no gravity in space.
An astronaut experiences weightlessness due the fact that as the spacecraft revolves around the Earth, the astronaut is continuously falling towards the Earth. This is similar to what a person standing in an elevator, that is falling freely, would experience. The person would be weightless as the elevator falls.

Read the assertion and reason carefully to mark the correct option out of the options given below :

Assertion : An astronaut in a satellite feels weightlessness.
Reason : As observed by another astronauts in the same satellite, force of gravity and centrifugal force balance each other.

physics gravitation: planets and satellites weightlessness application of newton's law of motion escape velocity

  1. If both assertion and reason are true and the
    reason is the correct explanation of the assertion

  2. If both assertion and reason are true but reason
    is not the correct explanation of the assertion

  3. If assertion is true but reason is false

  4. If assertion is false but reason is true

Show answer
Correct Option: A
Explanation:

In a satellite, weightlessness is felt.

The weight of a person in a satellite is balanced by the centrifugal force due to orbiting of the satellite around the earth, i.e.,
$mg=\dfrac{mv^2}{r}$