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

Step Ladder on a rough survace - torques help

  • Thread starter Bruno1983
  • Start date
  • #1
1
0

Homework Statement



A step ladder is moddelled as two model rods OA and Ab smoothly hinged at A. The other ends of the rods rest on a rough horizontal floor. The mass of rod AB is 4m and that of rod OA is m. The andle each rod makes with the vertical is theta. The origin is taken at O and the unit vectors i and j are defined as shown.

Here is a picture of the question
http://i93.photobucket.com/albums/l75/selah83/Q1.jpg [Broken]


Homework Equations



Torque = position vector * Force

The Attempt at a Solution



Ok a) is drawing the force diagram Iv got that down I think

B) Express each for in terms of i and j (Iv got that)
F1 = Friction acting on O = lF1l i
F2 = Friction acting on B = - lF2l i
N1 = Normal Reaction of OA = lN1l j
N2 = Normal Reaction of AB = lN2l j
W1 = Weight of rod OA = -lw1l j
W2 = Weight of rod AB = -lw2l j

but is says hence obtain two scalar equations relating to the magnitude of the forces when the system is in equilibrium. and then find the torque of each force about O.

I really dont understand this any help much appreciated!

Homework Statement





Homework Equations





The Attempt at a Solution

 
Last edited by a moderator:

Answers and Replies

  • #2
tiny-tim
Science Advisor
Homework Helper
25,832
249
Welcome to PF!

Hi Bruno1983! Welcome to PF! :smile:

(have a theta: θ :wink:)
A step ladder is moddelled as two model rods OA and Ab smoothly hinged at A. The other ends of the rods rest on a rough horizontal floor. The mass of rod AB is 4m and that of rod OA is m. The andle each rod makes with the vertical is theta. The origin is taken at O and the unit vectors i and j are defined as shown.

B) Express each for in terms of i and j (Iv got that)
F1 = Friction acting on O = lF1l i
F2 = Friction acting on B = - lF2l i
N1 = Normal Reaction of OA = lN1l j
N2 = Normal Reaction of AB = lN2l j
W1 = Weight of rod OA = -lw1l j
W2 = Weight of rod AB = -lw2l j

but is says hence obtain two scalar equations relating to the magnitude of the forces when the system is in equilibrium. and then find the torque of each force about O.
In this context, scalar means "not vector".

A vector equation would be ai + bj + ci + dj = 0, or (a,b) + (c,d) = 0

That can be decomposed into two scalar equations:

a + c = 0 and b + d = 0

Similarly you could decompose (a,b,c) x (d,e,f) = (u,v,w) into three scalar equations :wink:
 
Last edited:

Related Threads for: Step Ladder on a rough survace - torques help

  • Last Post
Replies
5
Views
925
  • Last Post
Replies
3
Views
4K
  • Last Post
Replies
4
Views
1K
  • Last Post
Replies
1
Views
3K
  • Last Post
Replies
9
Views
3K
  • Last Post
Replies
1
Views
1K
Replies
2
Views
887
Top