Really with this Free Response question for AP Physics

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Homework Help Overview

The problem involves a physics scenario with a ladder resting against a frictionless wall, where the forces acting on the ladder and the man climbing it need to be analyzed. The context is related to torque and equilibrium conditions in a mechanics problem.

Discussion Character

  • Exploratory, Conceptual clarification, Problem interpretation

Approaches and Questions Raised

  • Participants discuss identifying forces acting on the ladder and the importance of drawing a free body diagram. There are attempts to apply torque equations and conditions for equilibrium, but confusion arises regarding the actual friction force and the role of tension.

Discussion Status

The discussion reflects a mix of attempts to clarify the problem setup and the forces involved. Some participants express uncertainty about how to proceed, indicating a need for foundational understanding of free body diagrams and the forces at play.

Contextual Notes

Participants mention a lack of understanding regarding the drawing of diagrams and the identification of forces, which may be impacting their ability to solve the problem effectively. There is also a reference to a textbook that is not providing clarity.

AlphabetTown
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Homework Statement



1. An 80-kg man is one fourth of the way up a 10-m ladder that is resting against a smooth, frictionless wall. If the ladder has a mass of 20 kg and it makes an angle of 60° with the ground, find the force of friction of the ground on the ladder.



Homework Equations



T = Torque

∑T = T_{man} + T_{ladder} + T_{wall}

The Attempt at a Solution



Well I tried to find the Force of Friction F_{f} = μn; F_{f} = μmgcosθ:

mg = μmgcosθ
(20 kg)(-10 m/s^2) = μ(20 kg)(-10 m/s^2)cosθ
μ = 1.05

and

T = F*r*sinθ
T = (800 N)(10 m)(sin 60°)
T = -2438.5 N


I have no idea which of that is right. I only got 2 out of like 10 points for this Free Response question and I need to fix it, but I'm horrible at Physics and really need some help figuring it out. Thank you!
 
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(1) Start by identifying all the forces acting and drawing yourself a free body diagram.
(2) Careful! μN gives the maximum possible friction between surfaces, which is not what you want; You want the actual friction, which will be lower. Just label it Ff; you'll solve for it.
(3) Apply the conditions for equilibrium for both translation and rotation.
(4) Pick your 'axis' for calculating net torque wisely.
 
I'm sorry but that didn't help at all. I don't even know how to draw a free body diagram. I have absolutely no idea what to even do.
 
AlphabetTown said:
I'm sorry but that didn't help at all. I don't even know how to draw a free body diagram. I have absolutely no idea what to even do.
Do you have a textbook?

Draw a diagram of the ladder showing all the forces acting on it.
 
Yes and I've tried to use it but just makes no sense to me.

What are the forces? My guess would be normal force and the force of weight. What about tension? I never know whether to include that or not.
 

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