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Falling thin rod and angular speed

  • #1

Homework Statement


A 1.80 m long thing rod is balanced vertically on its tip on the floor. It starts to fall and its lower end does not slip. What is its angular speed just before it hits the floor?


Homework Equations


1/3ML^2
L=mvr


The Attempt at a Solution


When I first started this problem I had a better grasp, but as I started thinking about it I'm pretty sure I got further away. I started finding accelerations and velocities instead of getting back to the angular speed part of the problem. Now I'm trying to figure out how to actually do the problem. What is the first step?

Thanks.
 

Answers and Replies

  • #2
Hootenanny
Staff Emeritus
Science Advisor
Gold Member
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6

Homework Statement


A 1.80 m long thing rod is balanced vertically on its tip on the floor. It starts to fall and its lower end does not slip. What is its angular speed just before it hits the floor?


Homework Equations


1/3ML^2
L=mvr


The Attempt at a Solution


When I first started this problem I had a better grasp, but as I started thinking about it I'm pretty sure I got further away. I started finding accelerations and velocities instead of getting back to the angular speed part of the problem. Now I'm trying to figure out how to actually do the problem. What is the first step?

Thanks.
If the lower end does not slip, then you can treat it as a frictionless pivot. I would approach this problem using conservation of energy.
 
  • #3
Can you explain that a little further? I attempted to use conservation energy, but apparently I'm missing something somewhere along the way and not doing the problem correctly at all. Am I going to find the total kinetic energy of the rod, maybe some kind of K(transitional) + K(rotational) equation?

Thanks
 
  • #4
Hootenanny
Staff Emeritus
Science Advisor
Gold Member
9,622
6
Can you explain that a little further? I attempted to use conservation energy, but apparently I'm missing something somewhere along the way and not doing the problem correctly at all. Am I going to find the total kinetic energy of the rod, maybe some kind of K(transitional) + K(rotational) equation?

Thanks
At the beginning, just for the rod falls, what form is the energy in?
 

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