Understanding Physics: Gravitational Potential Energy

[t_n_p]

Homework Statement

http://img256.imageshack.us/img256/795/untitledpw7.jpg

The Attempt at a Solution

I know Ug stands for the gravitational potential energy, but I'm not sure what Us and Uint stands for.

At initial stage 1, I know the ball has kinetic energy and also has had work applied on it (the goalkeeper kicking the ball), but how do I know how much work is being applied?

 

[andrevdh]

You are in serious trouble with this question. I think you would need to consult your Physics handbook to solve it (or get help from the lecturer/other scolars in the class).

My guess is that the g refers to the Earth and the s refers to the soccer ball while the int refers to a change in internal potential energy. It is not clear (at all) what is on the x- and y-axii. That is why I think you should look in the handbook or ...

My take on it is that the goalkeeper injects energy into the ball/earth system by kicking it. If air friction were not present the sum of all energies would remain constant, but I have a sneaky fealing that in this case one should assume that air friction removes energy from the system.

 

[t_n_p]

LOL. Oh well, I tried!