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Homework Statement
You throw a rock of weight 20.4 N vertically into the air from ground level. You observe that when it is a height 14.9 m above the ground, it is traveling at a speed of 26.0 m/s upward.
Use the work-energy theorem to find its speed just as it left the ground;
Use the work-energy theorem to find its maximum height.
Take the free fall acceleration to be g = 9.80 m/s^2.
Homework Equations
Wtotal = delta K
K = mv^2
v^2 = vi^2 + 2a(x-xi)
The Attempt at a Solution
I believe this can also be done using kinematic equation, since we are given vf,x,a, and we want vi.
So if this is true, I will attempt both ways :D
26^2 = vi^2 + 2(-9.8)(14.9-0)
vi = 31.11 <--------> which is right
now, for using the work energy theorem.
we first need the mass.
using
w=mg
20.4 = m ( 9.8)
m = 2.08
K1 = 1.2(2.08)(v)^2
K2 = 1.2(2.08)(26)^2
K2 = 843.65
K1 = 0
...how do I proceed?