Introductory Torque Statics Problem

Join the discussion
Ask a follow-up here, or get your own question answered by working scientists, mathematicians and engineers — people, not an autocomplete.
Real named experts · corrections over time · the nuance an AI answer skips
1 reply · 2K views
JSmithDawg
Messages
9
Reaction score
0

Homework Statement


You're carrying a 4.0-m-long, 24kg pole to a construction site when you decide to stop for a rest. You place one end of the pole on a fence post and hold the other end of the pole 35 cm from its tip.

I've drawn a diagram of the problem on Paint...
upload_2015-2-9_19-15-51.png


Homework Equations


∑τ=0
τ=F⊥r

The Attempt at a Solution


I know that ∑τ=F(r1)+w(r2)+N(r3)=0, and I'm going to rewrite it so F(r1)+N(r3)=-w(r2). Now, if I call the left-most point the pivot point, my new equation becomes F(.35m)+4m(9.8 N/kg * 24kg) =-2m(-9.8 N/kg* 24 kg), which simplifies to F(.35m) = -470.4Nm, which makes F=-1344N. This seems way too big to be right; what did I do wrong?
 
Physics news on Phys.org
it would be much easier to use the RIGHTmost point as the pivot. Where is the weight applied? ... why are you not adding torques to zero? ...