Tag: introduction to gravitation

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Multiple choice physics universe and space heliocentric model introduction to gravitation introduction to gravity

Two solid spherical planets of equal radii R having masses 4 M and 9 M their centre are separated by a distance 6 R. A projectile of mass m is sent from the planet of mass 4 M towards the havier planet. what is the distance r of the point from the lighter planet where the gravitational force on the projectile is zero? 

  1. $1.4 R$
  2. $1.8 R$
  3. $1.5 R$
  4. $2.4 R$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

At the point where force is zero, the gravitational pull from both planets must be equal. G * 4M * m / r^2 = G * 9M * m / (6R - r)^2. Taking the square root: 2/r = 3/(6R - r). Solving gives 12R - 2r = 3r, so 5r = 12R, r = 2.4R.

Multiple choice physics universe and space heliocentric model introduction to gravitation introduction to gravity

If an orbiting satellite comes to a standstill suddenly,

  1. the satellite will move along the tangent.

  2. the satellite will move radically towards centre of the orbit.

  3. the satellite will go to outer space and will be lost.

  4. the satellite will continue to move in the same orbit.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

If the satellite is brought to standstill $v=0$ which gives the net force on the satellite=
$F=\dfrac{GMm}{{a}^{2}} $ in the direction of the centre of the earth which earlier was providing centripetal acceleration. So the satellite will fall on the earth

Multiple choice physics universe and space heliocentric model introduction to gravitation introduction to gravity

The moon revolves round the earth  $13$  times in one year. If the ratio of sun-earth distance to earth-moon distance is  $392,$  then the ratio of masses of sun and earth will be

  1. $365$
  2. $356 \times 10 ^ { - 12 }$
  3. $3.56 \times 10 ^ { 5 }$
  4. $1$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Using Kepler's Third Law and the relationship between orbital periods and distances, the ratio of the masses can be derived from the given orbital data.

Multiple choice physics universe and space heliocentric model introduction to gravitation introduction to gravity

Two spheres of masses $m$ and $M$ are situated in air and the gravitational force between them is $F$. The space around the masses is now filled with a liquid of specific gravity $3$. The gravitational force will now be

  1. $2 F$
  2. $F$
  3. $\displaystyle\frac {F}{3}$
  4. $\displaystyle \frac {F}{9}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The force of gravitation will be same as $F$ because gravitational force is dependent on the masses of the body and distance between them and does not depend on the medium between the masses.

Multiple choice physics universe and space heliocentric model introduction to gravitation introduction to gravity

The force acting on a mass of 1g due to the gravitational pull on the earth is called 1gwt. One gwt equals:

  1. 1 N

  2. 9.8 N

  3. 980 dyne

  4. none of these
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

1gwt is the force acting on a mass of $1g$ due to gravitational pull on earth

$1gwt=\frac{1}{1000}Kg \times 9.8ms^{-2}$
             =$9.8\times 10^{-3}N$
$1N=10^{5}dyne$
$9.8\times 10^{-3}N=980dyne$

$1gwt=980 dyne$

Multiple choice physics universe and space heliocentric model introduction to gravitation introduction to gravity

The gravitational force with which the earth attracts the moon :

  1. is less than the force with which the moon attracts the earth

  2. is equal to the force with which the moon attracts the earth

  3. is greater than the force with which the moon attracts the earth

  4. varies with the phases of the moon
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

By the Newton's gravitational law, the gravitational force between two bodies of masses $m _1$ and $m _2$ is given by $F=-\dfrac{Gm _1m _2}{r^2}$

where $r$ be the distance between them and negative sign indicates the attraction force. 
Thus, both of them attract each other with same force.

Multiple choice physics universe and space heliocentric model introduction to gravitation introduction to gravity
State whether true or false.
Gravitational forces can also be repulsive like that of electrostatic forces.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Gravitational force, $F=\cfrac { G{ M } _{ 1 }{ M } _{ 2 } }{ { R }^{ 2 } } $

Now the mass of the objects can not be opposite (i.e., mass cannot be negative), thus, the nature of the force cannot be repulsive like that of electrostatic force.

Multiple choice physics universe and space heliocentric model introduction to gravitation introduction to gravity

The mass of the moon is about $1.2$% of the mass of the earth. Compared to the gravitational force that earth exerts on the moon, the gravitational force the moon exerts on earth :

  1. is the same

  2. is smaller

  3. is greater

  4. Varies with its plane
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The gravitation force of attraction between two bodies is given by, $F=-\dfrac{Gm _1m _2}{r^2}$ where $G=$ gravitational constant, $m _1,m _2$  be the masses of bodies and $r$ be the distance between them.

As the force depends on the product of masses and distance between them, so same force will exert on each other.