Homework Help: What speed will the ball hit the ground?

1. Apr 17, 2012

SailorMoon01

A ball has a mass of 240g. (which would be 0.24kg?) is moving through the air at 20.0m/s with a gravitational potential energy of 70J. With what speed will the ball hit the ground.

Equations:

Ek=mv^2/2 (kinetic energy)
Eg=mgh (Gravitational potential energy)
Ek=mgxdisplacement (if you don't have velocity?)

I would appreciate ANY help...I don't get what I'm supposed to do.

P.S. the answer in the book says it should be 31.4m/s :)

2. Apr 17, 2012

dikmikkel

You assume that the groud is zero potential: Then the initian kinetic energy is $T_i =1/2mv_i^2$
And the initial potential energy is 70J the 70J is all being converted to kinetic energy when it falls so make your equation and solve it:
$E_{initial}= 70J+T_i = E_{final}$

3. Apr 18, 2012

Thank you :)