Hanging sign, torque and pivot points

  • Thread starter Sean77771
  • Start date
  • #1
22
0

Homework Statement



There is a sign of mass M that is attached to a rigid bar perpendicular to the ground. There is also a rope attached to the sign at the same point, then pulled out at an angle 45 degrees below the horizontal up to the ceiling.

a) Consider the rigid bar to be at equilibrium while the sign is hanging. What are the net force (in Newtons) and the net torque (in N m) acting on the bar?

b) Identify all forces that act on the bar. Write out an equation for the net force on the bar.

c) Choose the point where the bar meets the wall as a pivot point. Write out an equation for the net torque on the bar about that point.

d) Determine the magnitude of the tension in the rope. Take the mass of the sign to be 25kg, the mass of the bar is 5kg, and the length of the bar is 2m.

e) We could choose any point as the pivot and still get the same net torque. Why was the choice in part c a good choice for the pivot?

Homework Equations



T_net = Ia
when in equilibrium,
-- F_net = 0
-- T_net = 0

The Attempt at a Solution



I got that, for (a), these are both equal to zero, as the bar is in equilibrium...don't know where to go from here.
 

Answers and Replies

  • #2
Shooting Star
Homework Helper
1,977
4
If you give a rough diagram, I'm sure you'll get some responses. I am unable to visualize the whole picture.

Anyway, in all these kinds of statics problems, the way to proceed is to equate the sum of the horizontal and vertical forces individually to zero; and to equate the moment of all the forces about a conveniently chosen point to zero. Then solve the resulting equations.
 

Related Threads on Hanging sign, torque and pivot points

  • Last Post
Replies
1
Views
9K
  • Last Post
Replies
11
Views
15K
Replies
1
Views
3K
  • Last Post
Replies
1
Views
17K
Replies
2
Views
9K
Replies
12
Views
7K
Replies
4
Views
5K
Replies
1
Views
6K
Replies
9
Views
4K
  • Last Post
Replies
8
Views
2K
Top