# Homework Help: Combined rotational and translational motion

1. Sep 11, 2009

### e2m2a

1. The problem statement, all variables and given/known data

I need to determine the total kinetic energy of a long thin rod relative to a laboratory frame which rotates around an axis at an angular velocity w and the axis moves at a constant translational velocity. The mass of the rod is M and the length of the rod is L. The translational velocity of the axis is Vaxis.

2. Relevant equations
Moment of Inertia, I, of rod is: 1/3 M (L sq) (This is because the rod rotates at one end).

3. The attempt at a solution
I believe the total kinetic energy should be: Total KE = 1/2 M (Vaxis sq) + 1/2 I (w sq).
Is this correct?

2. Sep 16, 2009

### JANm

Hello e2m2a
The moment of inertia is correct and addition of energies too. Is there some relation of the tangential and the rotational velocities. Remind that the endpoint velocitie for a whip is one mach. The maximum is there when the endpoint of the rods velocity L*w adds up to Vaxis.
greetings Janm