Two particles of masses m₁ and m₂ attract each other gravitationally and are set in motion under the influence of the gravitational force? Will the centre of mass move?

1

(a)

Since, gravitational force is an internal force, therefore the centre of mass would not move.

Work done in moving a particle round a closed path under the action of gravitation force zero. Why?

1

(a)

Gravitational force is a conservative force which means that work done by it, is independent of path followed.

How much energy is required by a satellite to keep in orbiting?Neglect air resistance.

1

(a)

No energy is required.This is because the work done by centripetal force is zero.

An artificial satellite revolving around the earth does not need any fuel.On the other hand,the aeroplane requires fuel to fly at  certain height why?

1

(a)

The satellite move in air-free regions while the aeroplane has to overcome air resistance.

Assume that an artificial satellite release a bomb.Would the bomb ever strike the earth if the effect of air resistance in neglected?

1

(a)

The bomb would merely act as another satellite.It would never hit the earth due to state of weight lessness.