Tag: introduction to gravity

Questions Related to 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? 

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

  1. $1.4 R$

  2. $1.8 R$

  3. $1.5 R$

  4. $2.4 R$

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Correct Option: D

If an orbiting satellite comes to a standstill suddenly,

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

  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.

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Correct Option: B
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

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

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

  1. $365$

  2. $356 \times 10 ^ { - 12 }$

  3. $3.56 \times 10 ^ { 5 }$

  4. $1$

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Correct Option: C

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

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

  1. $2 F$

  2. $F$

  3. $\displaystyle\frac {F}{3}$

  4. $\displaystyle \frac {F}{9}$

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Correct Option: B
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.

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

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

  1. 1 N

  2. 9.8 N

  3. 980 dyne

  4. none of these

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Correct Option: C
Explanation:

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

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

$1gwt=980 dyne$

The motion of planets in the solar system is an exampIe of the conservation of

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

  1. mass

  2. linear momentum

  3. angular momentum

  4. energy

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Correct Option: C
Explanation:

For any circular motion the angular momentum is conserved as no torque is acting on it because centripetal force acts through the point of axis.

$1 kgf =$

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

  1. $1 gf$

  2. $10 gf$

  3. $100 gf$

  4. $1000 gf$

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Correct Option: D
Explanation:

$1 kgf = 9.8 N =9.8 \times {10}^{5}dyne=980 \ times 1000 dyne=1000 \times (980dyne)=1000gf$

The gravitational force with which the earth attracts the moon :

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

  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

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Correct Option: B
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.

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

  1. True

  2. False

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Correct Option: B
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.

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 :

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

  1. is the same

  2. is smaller

  3. is greater

  4. Varies with its plane

Show answer
Correct Option: A
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.