(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

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.

2. Relevant equations

Wtotal = delta K

K = mv^2

v^2 = vi^2 + 2a(x-xi)

3. 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?

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# Homework Help: Work Energy Theorem and speed

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