• Support PF! Buy your school textbooks, materials and every day products Here!

Lagrangian Mechanics with one constraint

  • Thread starter Natchanon
  • Start date
  • #1
31
3

Homework Statement


slab.PNG
r.PNG

slab.PNG
I'm supposed to find the normal force acting on the box by the slab as a function of time. The problem is I don't know what the constraint is. I can't find the relation between r and theta that adds the two up to zero.

Homework Equations


upload_2018-10-21_17-21-57.png

Lagrangian equation.

The Attempt at a Solution


I tried constraint f(r, theta , t) = theta and got lamda = mr (gcos(theta) + r theta(double dot) ) = mgrcos(theta) since omega is constant, but still couldn't get the right answer.
 

Attachments

Answers and Replies

  • #2
TSny
Homework Helper
Gold Member
12,405
2,841
Hello, and welcome to PF.

If you know ##r## and ##\theta## as functions of time, then I don't understand why you would need to bother with setting up the Lagrangian. Did you state the problem word-for-word as given to you?
 
  • #3
31
3
Hello, and welcome to PF.

If you know ##r## and ##\theta## as functions of time, then I don't understand why you would need to bother with setting up the Lagrangian. Did you state the problem word-for-word as given to you?
Sorry for the late reply. I was able to figure it out. Thank you.
 

Related Threads on Lagrangian Mechanics with one constraint

Replies
2
Views
325
Replies
2
Views
436
Replies
1
Views
1K
  • Last Post
Replies
3
Views
763
  • Last Post
Replies
1
Views
1K
  • Last Post
Replies
3
Views
3K
  • Last Post
Replies
10
Views
3K
  • Last Post
Replies
1
Views
1K
  • Last Post
Replies
0
Views
2K
Top