posted by anton .
You throw a 20-N rock vertically into the air from ground level. You observe that when it is 15.0 m above the ground, it is travelling at 25.0 m/s upward. Use the work-energy theorem to find a) its speed just as it left the ground; b) its maximum height.
work-energy theorem: W=K2-K1
this simplifies to 2(-g)h=V2^2-V1^2
now all you have to do is plug in numbers.
max height is where V=0
we can use the work-energy theorem again.
this time we get: 2(-g)h=0-30.32^2
so, max h=-(30.32^2)/2(-g)=46.90m
the final answer is:
max height = 46.90m
and initial velocity = 30.32m/s