Another torque/statics problem

  • Thread starter Thread starter blue2004STi
  • Start date Start date
Join the discussion
Registration is free. Ask a follow-up in this thread, or start your own.
4 replies · 6K views
blue2004STi
Messages
21
Reaction score
0

Homework Statement


Prof. Holland, in his younger days, (when he had a mass of 55kg) is in a lie-back climb along a fissure, with hands pulling on one side of the fissure and feet pressed against the opposite side. The fissure has width w = 0.25m, and the center of mass of the climber is a horizontal distance d = 0.43m from the fissure. The coefficient of static friction between hands and rock, μhands, is 0.42, and between boots and rock, μboots is 1.25.
What is the least horizontal pull by the hands and push by the feet that will keep him stable?



Homework Equations


Weight: 0 = (Ushands*Fa + Usboots*Fb) -539N
Fb=force by boots
Fa=force by hands
Torque: 0 = Fa*Distance from CM + Fb*Distance from CM




The Attempt at a Solution


So I tried setting up an equation for the forces made by the hands and feet which was the "Weight" equation above. Then I created the "Torque" equation. I knew since the climber(Professor Holland) was in static equilibrium that the both of them had to equal zero. I solved for both of the forces and keep coming up with A=786.6369N and B=166.89N and A+B(what they're looking for)=953.5269N.

I have to submit it online and it says that the answer is not correct. What am I doing wrong? I don't understand this problem!AHHHHH!

Thanks,
Matt

oh yeah forgot, thanks in advance for the help...it's much needed.:smile:
 
Last edited:
Physics news on Phys.org
We need a diagram. I can't picture at all what you mean. Not being a rock climber.
 
13-34.jpg


Sorry about the no picture thing, hopefully this works.
 
In the torque equation, try leaving out the u's. The force normal to the frictional force is the one causing the torque ( I think).
 
Woops, I forgot to delete the U's from that equation when I put it up here, I'll edit the first post. I didn't include U's in torque, at least it doesn't look like I did. Sorry