Physics Help. I really need help on this question. Please.

Question

What can be said about the total energy and work if we looked at the system as the ball + earth instead of just the ball.

Answer 1

I am not quite sure how to answer this question, but here is my explanation:

 

The total energy of a system is the combination of kinetic energy and Rolling energy

 

Total energy = 1/2 m v²+1/2 Iω² 

 

The ball alone is a mass that has no energy without the earth. when laid at rest on the earth it is attracted to the center of the earth by the force of gravity F = mg where g is the gravitational acceleration, However the ball will remain motionless until an external force is exerted on it and will set it into motion. The total energy of the ball is both its kinetic energy and rolling energy. 

 

When the ball is lifted up to a certain elevation, it now has a potential energy. PE = mgh with a magnitude that increases with the height of the ball and a constant earth gravitational acceleration g = 9.8 m/s², please note that again without the force of gravity between the ball and the earth, there is no potential energy. when the ball is dropped the potential energy converts to kinetic energy when the ball reaches the earth based on conservation of energy principle. The bottom line of all this discussion is that earth gravity is the force that causes the ball to drop or roll. the ball alone has no energy, but the ball and earth is the system that generates both work and energy. I hope this helps.