Help With A Concept on Work: Should be Easy

[cheechnchong]

A 0.6 kg baseball is dropped out of a window that is 6.1 m above the ground. The ball is caught by a person whose hands are 1.5m above the ground.

Questions
What is the gravitational potential energy of the baseball, relative to the ground
--When it is caught? (Is this -27.05 J ?)
--when it is released? (Is this 0 J ?)

just need some clarification...i already solved most of the problem so that I am not struggling with! THANKS erryone

 

[berkeman]

They say relative to the ground, so the PE gained by the ball is the work put into it to raise it from the ground to those two heights listed.

 

[cheechnchong]

The say relative to the ground, so the PE gained by the ball is the work put into it to raise it from the ground to those two heights listed.

I'm sorry...by your post I am totally lost! All i need to know is if I am right or wrong? because if I am right, then i know the conceptual approach to this kinda question...

 

[radou]

I'm sorry...by your post I am totally lost! All i need to know is if I am right or wrong? because if I am right, then i know the conceptual approach to this kinda question...

While dealing with potential energy, you have to define the 'zero level' of potential energy. In your problem it is said 'relative to the ground', so this makes the ground your 'zero level'. Now, what is the definition of gravitational potential energy? Just plug in the two heights into the definition. The results you got don't look correct to me, btw.

(The result you got for a) (only it's positive) is what is stated in the post above by berkeman - the work done by the force of gravity equals the change of potential energy, which is the difference in the potential energy between the position at the window and in the hands.)