What is the rotational kinetic energy?

[MillerGenuine]

Homework Statement

Uniform density rod with mass 1.2 kg, length 0.7m rotates around an axis perpendicular to the rod, with angular speed 50 rad/sec. its center moves with a speed of 8m/s.
What is the rotational kinetic energy?

Homework Equations

K= 1/2 I * V^2 (V is angular speed, 50 rad/s)

I_cylinder = 1/12 ML^2 + 1/4MR^2

The Attempt at a Solution

I can't seem to find my radius. I am assuming you find it by using the velocity of the center?

 

[tiny-tim]

Hi MillerGenuine!

(try using the X² icon just above the Reply box )

I_cylinder = 1/12 ML^2 + 1/4MR^2
…
I can't seem to find my radius.

In exam questions, a rod (like a cable or a string) can be assumed to have zero radius …

just use 1/12 ML² ​