# Q&A - Ask Doubts and Get Answers

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A body weighs 200 N on the surface of the earth  how much will it weigh at half way down to the center of the earth ?

• Option 1)

150 N

• Option 2)

200 N

• Option 3)

250 N

• Option 4)

100 N

Option 1) 150 N  Option 2) 200 N  Option 3) 250 N  Option 4) 100 N

The work done to raise a mass m from the surface of the earth to a height h, which is equal to the radius of the earth is :

• Option 1)

mgR

• Option 2)

2 mgR

• Option 3)

1/2 mgR

• Option 4)

3/2 mgR

Option 1) mgR  Option 2) 2 mgR  Option 3) 1/2 mgR  Option 4) 3/2 mgR
Two spherical bodies of mass M and 5 M and radii R and 2 R are released in free space with initial separation between their centres equal to 12 R If they attract each other due
to gravitational force only, then the distance covered by the smaller body before collision is:
a) 7.5 R
c)25R
b) 1.5 R
d) 4.5 R

appropriate ans?

An artificial satellite is moving around earth in a circular orbit with speed equal to one fourth the escape speed
of a body from the surface of earth. The height of satellite above earth's surface is (R is radius of earth)

@ABHISHEK escape speed of a body= and orbital speed of a body= but here  so  So  r=R+h so h=7R
e â€¢ 10:24 At the centre a Exam Videos Question Questions Books Asked in: AIPMT-2010 A particle of mass M is situated at the centre of a spherical shell of same mass and radius a. The gravitational potential at a point situated at a/2 distance fr0m the centre, will be:
The gravitational potential at a point situated at a/2 distance from the centre, will be:

Please explain me "Universal gravitational constant".

The value of the gravitational constant G entering the Universal law of gravitation can be determined experimentally and this was first done by English scientist Henry Cavendish in 1798.   The bar AB has two small lead spheres attached at its ends. The bar is suspended from a rigid support by a fine wire. Two large lead spheres are brought close to the small ones but on opposite sides as shown....
Medical
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If the mass of the Sun were ten times smaller and the universal gravitational constant were ten times larger in magnitude, which of the following is not correct ?

• Option 1)

Time period of a simple pendulum on the Earth would decrease.

• Option 2)

Walking on the ground would become more difficult.

• Option 3)

Raindrops will fall faster.

• Option 4)

'g' on the Earth will not change.

As we have learned Acceleration due to gravity (g) - Force extended by earth on a body is gravity. Formula:    gravity density of earth Radius of earth   - wherein It's average value is on the surface of earth   For earth     rain drop will fall faster walking on the ground become more difficult  Time period of  simple pendulum will decrease           Option 1) Time period of a...
Medical
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The kinetic energies of a planet in an elliptical orbit about the Sun, at positions A, B and C are KA, KB and KC, respectively. AC is the major axis and SB is perpendicular to AC at the position of the Sun S as shown in the figure. Then

• Option 1)

$K_{B}

• Option 2)

$K_{A}>K_{B}>K_{C}$

• Option 3)

$K_{A}

• Option 4)

$K_{B}>K_{A}>K_{C}$

Option 2

Medical
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Two spherical bodies of mass M and 5 M and radii R and 2R released in free space with initial separation between their centres equal to 12 R. If they attract each other due to gravitational force only, then the distance covered by smaller body before collision is

• Option 1)

4.5 R

• Option 2)

7.5 R

• Option 3)

1.5 R

• Option 4)

2.5 R

As we learnt Properties of Gravitational Force - (i) Always attractive (ii) It is central force (iii) Weakest force   - wherein Ratio of    between two electrons  is  As their centre of mass remains unchanged     or   Option 1) 4.5 R Incorrect Option Option 2) 7.5 R Correct Option Option 3) 1.5 R Incorrect Option Option 4) 2.5 R Incorrect Option
Medical
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The radii of circular orbits of two satellites A and B of the earth, are 4 R and R, respectively. If the speed of satellite A is 3 V, then the speed of satellite B will be:

• Option 1)

3 V/4

• Option 2)

6 V

• Option 3)

12 V

• Option 4)

3 V/2

Orbital velocity of satellite -  Position of satellite from the centre of earth  Orbital velocity - wherein The velocity required to put the satellite into its orbit around the earth.    Foe satelite A        For satelite B          Option 1) 3 V/4 Incorrect Option Option 2) 6 V Correct Option Option 3) 12 V Incorrect Option Option 4) 3 V/2 Incorrect Option
Medical
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Dependence of intensity of gravitational field (E) of earth with distance (r) from centre of earth is correctly represented by

• Option 1)

• Option 2)

• Option 3)

• Option 4)

As we learnt in Gravitational field intensity due to Uniform solid sphere - Outside surface  * on the surface - wherein * Inside surface         Intensity due to spherical shell -  Radius of shell  Position of Pt.  Mass of spherical shell - wherein Outside the surface  on the surface inside the surface      For the point inside the earth ( r < R) At centre r = 0                E =...
Medical
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A planet moving along an elliptical orbit is closest to the sun at a distance of $r_{1}$ and farthest away at a distance of r2. If $V_{1}$ and $V_{2}$ are the linear velocities at these points respectively, then the ratio $\frac{V_{1}}{V_{2}}$ is

• Option 1)

$(r_{1}/r_{2})^{2}$

• Option 2)

$r_{2}/r_{1}$

• Option 3)

$(r_{2}/ r_{1})^{2}$

• Option 4)

$r_{1}/r_{2}$

As we discussed in concept ID Angular momentum of satellite -  Angular momentum  mass of satellite - wherein depends on both the masses , mass of centre of body and mass of planet as well as radius of earth.    According to conservation of Angular momentum Option 1) Incorrect Option Option 2) Correct Option Option 3) Incorrect Option Option 4) Incorrect Option
Medical
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A particle of mass m is thrown upwards from the surface of the earth, with a velocity u. The mass and the radius of the earth are, respectively, M and R. G is gravitational constant and g is acceleration  due to gravity on the surface of the earth. The minimum value of u so that the particle does not return back to earth is

• Option 1)

$\sqrt{\frac {2GM}{R}}$

• Option 2)

$\sqrt{\frac{2GM}{R^{2}}}$

• Option 3)

$\sqrt{2gR^{2}}$

• Option 4)

$\sqrt{\frac{2GM}{R^{2}}}$

As we learnt Relation of escape velocity and orbital velocity -  Orbital velocity  Escape velocity - wherein    According to law of conservation of machanical energy Option 1) Correct Option Option 2) Incorrect Option Option 3) Incorrect Option Option 4) Incorrect Option
Medical
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A particle of mass M is situated at the centre of a spherical shell of same mass and radius a. The gravitational potential at a point situated at $\frac{a}{2}$ distance frim the centre, will be:

• Option 1)

$\frac {-3GM}{a}$

• Option 2)

$\frac{-2GM}{a}$

• Option 3)

$\frac{-GM}{a}$

• Option 4)

$\frac{-4GM}{a}$

As we learnt Potential due to Uniform Ring -  distance from ring  radius of Ring  Potential    - wherein At a point on its Axis  At the centre    Option 1) Correct Optino Option 2) Incorrect Option Option 3) Incorrect Option Option 4) Incorrect Option
Medical
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A black hole is an object whose gravitational field is so strong that even light cannot escape from it. To what approximately radius would earth (mass=5.98X$10^{24} kg$) have to be compressed to be a black hole?

• Option 1)

$10^{-9}m$

• Option 2)

$10^{-6} m$

• Option 3)

$10^{-2} m$

• Option 4)

100m

As we learnt in Escape velocity ( in terms of radius of planet) -  Escape velocity Radius of earth - wherein depends on the reference body greater the value of  or  greater will be the escape velocity   For earth     Option 1) Incorrect Option Option 2) Incorrect Option Option 3) Correct Option Option 4) 100m Incorrect Option
Medical
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The ratio of escape velocity of earth   to the escape velocity at a planet whose radius and mean density are twice as that of earth is:

• Option 1)

1 : 2

• Option 2)

• Option 3)

1 : 4

• Option 4)

Escape velocity ( in terms of radius of planet) -  Escape velocity Radius of earth - wherein depends on the reference body greater the value of  or  greater will be the escape velocity   For earth    escape velocity= Option 1) 1 : 2 This option is incorrect  Option 2) This option is correct  Option 3) 1 : 4 This option is incorrect  Option 4) This option is incorrect
Medical
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Starting from the centre of the earth having radius R, the variation of (acceleration due to gravity) is shown by

• Option 1)

• Option 2)

• Option 3)

• Option 4)

Acceleration due to gravity inside the earth surface  and acceleration due to gravity outside earth surface  Option 1) This option is incorrect. Option 2) This option is correct. Option 3) This option is incorrect. Option 4) This option is incorrect.
Medical
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At what height from the surface of earth the gravitation potential and the value of g are -5.4 107 J kg-2 and 6.0ms-2  respectively? Take the radius of earth as 6400 km:

• Option 1)

2600 km

• Option 2)

1600 km

• Option 3)

1400 km

• Option 4)

2000 km

Potential due to Uniform solid sphere -  Radius of sphere  Mass of sphere  distance from centre of sphere - wherein Outside the surface on the surface Inside the surface      Gravitational potential at a height    acceleration due to gravity at the height =                                                                      or  or  or  or   Option 1) 2600 km This option is...
Medical
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Two astronauts are floating in gravitational free space after having lost contact with their spaceship. The two will:

• Option 1)

keep floating at the same distance between them.

• Option 2)

move towards each other.

• Option 3)

move away from each other.

• Option 4)

will become stationary.

The two astronauts will move towards each other due to the gravitational force of attraction. Option 1) keep floating at the same distance between them. This option is incorrect. Option 2) move towards each other. This option is correct. Option 3) move away from each other. This option is incorrect. Option 4) will become stationary. This option is incorrect.
Medical
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A satellite of mass m is orbiting the earth (of radius R) at a height h from its surface. The total energy of the satellite in terms of g0, the value of acceleration due to gravity at the earth's surface, is

• Option 1)

• Option 2)

• Option 3)

• Option 4)

Gravitational potential energy at height 'h' -  Potential energy at height   Radius of earth - wherein    total energy of satelliteis equal to half of its potential energy.   or       Option 1) This option is incorrect Option 2) this option is correct. Option 3) This option is incorrect. Option 4) this option is incorrect.
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