# Homework Help: Work of a uniform rod

1. Nov 8, 2005

### SoccaCrazy24

here is the problem...

How much work must be done to accelerate a baton from rest to an angular speed of 5.6 rad/s about its center? Consider the baton to be a uniform rod of length 0.49 m and mass 0.46 kg.

Mrod=0.46kg
Lrod=0.49m

Well i know that W=T*(change in theta)

T=I*w

I=(1/12)M*L^2
I=0.0092038 (kg*m2)

so for w in the equation would i use wf? or average w?
*using wf
T=.05154 (N*m)
*using w average
T=.02577 (N*m)

so which T would I use in solving for Work....? and supposing that I find the change in theta....

2. Nov 8, 2005

### SoccaCrazy24

anyone got anythign to say to help me or no?

3. Nov 10, 2005

### lightgrav

The Work is supposed to CHANGE the KE
during a process.
The starting KE = 0 , with w = 0
But the ending KE = ½ I w^2
(formula "looks like" KE for linear motion!)

Torque is not Iw , Torque is = I alpha
so is I times the CHANGE in w / Change in time.
Use Work & Energy approach to avoid having to calculate time.

The Work done is for the entire process.
The starting condition is at the start of the process,
the ending condition is at the end of the process.