Conservation of Energy for a rotating Rod

  • Thread starter AROD
  • Start date
  • #1
18
0

Homework Statement


rod%20problem.jpg



Homework Equations



Rotational Kinetic Energy = 1/2*I*w^2

The Attempt at a Solution



I was just wondering if someone explain to me why the potential energy is MgL/2 ?

Is this not the same for the torque from gravity?
 

Answers and Replies

  • #2
220
0
As the hint in a) states, you can neglect the mass m. And since the mass M is uniform, you can presume all its weight is in the center, hence MgL/2
 
  • #3
126
0
Because the rod's center of mass is placed at L/2 over the ground.

Edit: oops, already answered :)
 
  • #4
Doc Al
Mentor
44,957
1,220
I was just wondering if someone explain to me why the potential energy is MgL/2 ?
The rod is uniform. Where is its center of mass?
Is this not the same for the torque from gravity?
The torque from gravity about the pivot point depends upon the angle of the rod.

Edit: Already answered twice!
 
  • #5
18
0
ok so then its just mgh with h = L/2 . that makes sense

then as it tips the hypotoneuse would be L/2, and the height would be this times the cos of theta.

thanks
 

Related Threads on Conservation of Energy for a rotating Rod

  • Last Post
Replies
1
Views
8K
  • Last Post
Replies
21
Views
3K
  • Last Post
Replies
2
Views
5K
  • Last Post
Replies
1
Views
2K
  • Last Post
Replies
3
Views
2K
  • Last Post
Replies
1
Views
2K
  • Last Post
Replies
6
Views
5K
Replies
12
Views
6K
Top