- #1
Hans Herland
- 17
- 1
Homework Statement
Determine the smallest force P that will cause the spool to have impending motion.
Homework Equations
Equations of equilibrium, and static frictional equations.
##ΣFx = 0;##
##ΣFy = 0;##
##ΣMb = 0;##
##Fsa = μNa##
##Fsb = μNb##
The Attempt at a Solution
My first problem here is properly identifying the forces at work, specifically, the forces at point B. I've made a drawing that shows how I think the forces apply at these points:
##G = mg = 150 * 9.81 = 1471.5N##
This makes my equations of equilibrium as follows:
##ΣFx = 0; P - Fsa - Fsb cos 51.3 - Nb sin 51.3 = 0##
##ΣFy = 0; Na + Nb cos 51.3 - Fsb sin 51.3 - 1471.5N = 0##
##ΣMb = 0; P(0.45) + Fsa(0.15) + Na(0.312) - 1471.5(0.312) = 0##
##Fsa = 0.4 * Na##
##Fsb = 0.2 * Nb##
I selected the moment equation to be set around point B, as this seems to give me the equation with the least amount of unknowns, but I've also tried to solve the problem where I look at the moment around point A instead.
So as for the first problem I'm facing: Have I correctly identified the forces at play?
If I have, do my equations of equilibrium look correct? I've failed to be able to work with the equations to find any of the unknows I need to continue.
Thanks for any help.