# Rotational Kinematics of a thin rod

1. Jul 31, 2009

### Cheddar

1. The problem statement, all variables and given/known data
A thin rod (length = 1.50 m) is oriented vertically, with its bottom end attached to the floor by means of a frictionless hinge. The mass of the rod may be ignored, compared to the mass of the object fixed to the top of the rod. The rod, starting from rest, tips over and rotates downward. (a) What is the angular speed of the rod just before it strikes the floor? (b) What is the magnitude of the angular acceleration of the rod just before it strikes the floor?

2. Relevant equations
No clue.

3. The attempt at a solution
radius = 1.50 m
angular displacement = 90 degrees
Any suggestion as to where to start would be great...
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Jul 31, 2009

### Staff: Mentor

Hints:
(a) Consider energy conservation. How would you write the rotational kinetic energy of this object?
(b) What's the torque on the object?