ok now so to find the GPE of a 80kg dive who jumped from a 10 m high plat form i take 80 x 9.8 x 10 but do i divide it by 2 if it wants to know what the GPE is half way down????????
Since P.E. depends upon height, if it's halfways down, it's P.E. will only be one-half of what it was.
+20 
