Question

Suppose gravity of the earth suddenly becomes zero, then in which direction will the moon begin to move if no other celestial body affects it?

Answer 1

Hint: To study this effect of centripetal force we have to learn about centripetal forces which are responsible for circular motion of anybody in the orbit and without this force body cannot be able to do circular motion and this force is always produced by some other force acting towards the centre of that orbit.

Complete step by step answer:
Whenever a body is performing circular motion the centripetal force is required without this force body cannot do circular motion and this force is always directed towards the centre like an earth revolves around the sun and for circular motion centripetal force is required which produces by gravitational forces .Like in the same way due to gravity , the moon will also move around earth in a circular orbit due to gravitational forces acts like a centripetal force and its direction is towards the centre of circular orbit.
As according to the question when the gravity of earth suddenly becomes zero or diminishes then the moon will not able to move in circular orbit because gravity makes planet to revolve around that orbit so moon will begin to move in a straight line in the direction in which it was moving at that instant because the circular motion of moon is due to the centripetal force provided by the gravitational force of earth and if the gravitational force becomes zero then it means no centripetal force is there to help the moon to move in the circular orbit. Therefore it will move in a straight line. So centripetal force is only responsible for circular motion.
We can conclude this by saying that in the absence of gravity of earth; gravitation forces are also absent then the direction of motion of the moon is straight line not circular because no centripetal force acts on it and no other celestial body affects it.

Note: When body is performing circular motion then tangent at any point will give the direction of velocity and centripetal force and always acting towards the centre from each point such that velocity and centripetal forces are perpendicular to each other so work done by that force is calculated to be zero.