A force when applied on a rigid object does not change the inter-spacing between its constituent particles and therefore it does not change the dimensions of the object, but causes motion in it.
On the other hand, a force when applied on a non-rigid object, change the inter-spacing between its constituent’s particles and therefore cause a change in its dimensions. 

 
where, 

The weight of a body placed at the centre of the earth is zero. 

Yes. The velocity of particle in circular motion is variable or the circular motion is accelerated even though the speed of particle is uniform. 
The velocity vector is constant in magnitude but changing in direction. Since the direction changes, acceleration is not unifrom. 

i) Work is said to be done only when the force applied on a body makes the body move, that is, there is displacement of the body.

ii) The work done by the moon when it revolves around the earth is zero. This is because the work done for a closed path is zero.