Another torque/statics problem

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Homework Help Overview

The problem involves a climber's static equilibrium while performing a lie-back climb in a fissure. The scenario includes specific measurements for the climber's mass, the fissure's width, the distances involved, and the coefficients of static friction for hands and feet. The objective is to determine the minimum forces exerted by the hands and feet to maintain stability.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • The original poster attempts to set up equations for forces and torque to solve for the required forces. Some participants suggest the need for a diagram to better understand the problem setup. Others propose reconsidering the torque equation by focusing on the forces causing torque rather than including coefficients of friction.

Discussion Status

The discussion is ongoing, with participants exploring different interpretations of the problem and suggesting adjustments to the equations used. There is no explicit consensus on the correct approach yet, but guidance has been offered regarding the torque equation.

Contextual Notes

The original poster expresses confusion about the problem and notes that their submitted answer was marked incorrect, indicating potential misunderstandings in their calculations or setup. There is also mention of a lack of visual aids to clarify the scenario.

blue2004STi
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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:
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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
 

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