# Homework Help: Applying the work-energy theorem

1. Oct 15, 2008

### hpnhpluv

1. The problem statement, all variables and given/known data
Use the work-energy theorem to solve.
A branch falls from the top of a 95 m tall tree, starting from rest. How fast is it moving when it reaches the ground? Neglect air resistance.

2. Relevant equations
work-energy theorem:w_total=K_2-K_1
In this problem, K_1 is 0 since it is starting from rest.
K_2=(1/2)*m*v^2 (?)
w=fd (relevant?)

3. The attempt at a solution
If I use the equations I have above, I end up with w=1/2*m*v_f^2.
However, I am not given a mass. I do not know how to finish the calculation without a mass.
If I use w=fd, I have (9.8 m/s^2)(mass)*(95 m).
I am really stuck.

2. Oct 16, 2008

### atyy

In addition to the equations you listed, you also need the equation for the force of gravity on a mass.

You are only asked for the final velocity. Assume a mass, and carry through with the equations. Hopefully the mass will cancel out when you solve for the velocity.