Energy Conservation, Question on kinetic and potential

Hey there,

so a hockey ball is held 2 metres above the ground and has 3.2 joules of gravitational potential energy. It is then dropped...

how much kinetic energy does it have before it reaches the ground?

cheers thank you!

Increasingly more than its potential energy when it was dropped.

Beyond that I cannot calculate an answer because I dropped my calculator from an equal height as the part of my brain that formulates and solves equations - I'm pretty sure they hit the ground and broke at the same moment though

This post has been edited by light in the tunnel on Nov 2 2009, 01:12 AM

The important thing about these types of problems is where you define your zero to be. If you're holding your ball of mass m at some height h then the GPE it has is mgh. The height is defined with respect to some zero point which is normally the ground (this isn't always the case though).

In your example, if the zero point is the ground and you've worked everything out correctly (I haven't checked) as the ball drops GPE is changed to kinetic energy. As it hits the ground all of the GPE has become KE so it will have 3.2 J of KE.