How Do You Calculate the Height of a Rock at Half Its Initial Speed?

[BRETTISRAD]

ok you have a rock of mass 22.8 KG
It has an initial KE of 28 Joules
This rock is thrown upwards with an initial velocity of 1.56721 m/s
It peak height is .122807 ( i hope that's right )
What is the height of the rock at half its initial speed?
If someone could just give me the right formula or head me in the right direction that would be great. :D

 

[Doc Al]

One way is to use conservation of energy. As it rises, it loses KE (figure out how much) and gains PE.

Another way is to use kinematics: $v_f^2 = v_i^2 + 2ad$

 

[BRETTISRAD]

Thankyou, got it with conservation of energy. :D