The distance between the centres of moon and earth is D. The mass of earth is 81 times the mass of the moon. At what distance from the centre of the earth the gravitational force will be zero ?

1. $\frac{D}{2}$                                2. $\frac{2D}{2}$                                

3. $\frac{4D}{3}$                              4. $\frac{9D}{10}$

3 particles each of mass m are kept at vertices of an equilateral triangle of side L. The gravitational field at centre due to these particles is

1. zero                                                                       

2. $\frac{3GM}{L^2}$

3. $\frac{9GM}{L^2}$                                                                     

4. $\frac{12}{\sqrt{3}}\frac{GM}{L^2}$

The centripetal force acting on a satellite orbiting around the earth and the gravitational force of the earth acting on the satellite, both are equal to \(F\). The net force on the satellite is:
1. zero
2. \(F\)
3. \(F\sqrt{2}\)
4. \(2F\)

Two sphere of mass 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. F                                        

2. $\frac{F}{3}$  

3. $\frac{F}{9}$                                      

4. 3 F

Two identical solid copper spheres of radius \(R\) are placed in contact with each other. The gravitational attraction between them is proportional to:
1. \(R^2\)
2. \(R^{-2}\)
3. \(R^4\)
4. \(R^{-4}\)

An astronaut orbiting the earth in a circular orbit 120 km above the surface of the earth, gently drops a spoon out of the spaceship. The spoon will:

1. Fall vertically down to the earth

2. Move towards the moon

3. Will move along with space-ship

4. Will move in an irregular way then fall down

Imagine a light planet revolving around a very massive star in a circular orbit of radius R with a period of revolution T. If the gravitational force of attraction between planet and star is proportional to ${\mathrm{R}}^{\frac{-5}{2}}$, then ${\mathrm{T}}^2$ is proportional to:

1. ${\mathrm{R}}^3$                               

2. ${\mathrm{R}}^{7/2_{}^{}}$

3. ${\mathrm{R}}^{5/2}$                           

4. ${\mathrm{R}}^{3/2}$

A mass M is split into two parts, m and (M–m), which are then separated by a certain distance. What ratio of m/M maximizes the gravitational force between the two parts

1. 1/3                           

2. 1/2

3. 1/4                           

4. 1/5

Two identical satellites are at R and 7R away from the earth surface, the wrong statement is (R = Radius of the earth)

1. Ratio of total energy will be 4

2. Ratio of kinetic energies will be 4

3. Ratio of potential energies will be 4

4. Ratio of total energy will be 4 but ratio of potential and kinetic energies will be 2

A body of mass m is taken from earth's surface to the height h equal to the radius of the earth, the increase in potential energy will be:

1. mgR                                

2. $\frac{1}{2}$mgR

3. 2mgR                             

4. $\frac{1}{4}$ mgR