What were my mistakes in solving this ladder problem in physics?

Thread starter Icefire_16
Start date Jan 15, 2020
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Physics

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The discussion focuses on a physics problem involving a ladder, where the user calculated the normal force using a formula but arrived at an incorrect answer. The user provided their equation for normal force, Fnormal = ((mg1d1) + (m2gd2)) / d3, and substituted values but did not achieve the expected result. Key variables mentioned include distances (d, d1, d2, d3) and masses (m, m2), with a request for clarification on torque axis choice. There is confusion regarding the notation of Fn, which appears to represent the normal force but is also referred to as friction. The thread seeks to identify mistakes in the calculations and clarify variable definitions.

Jan 15, 2020

Icefire_16

Homework Statement: A 400N woman climbs a 100N, 10m ladder inclined at an angle of Θ = 60°. When she is 3m away from the wall, how much friction is needed at point A to keep the ladder from slipping. (Assume theres no friction between wall and ladder.) (Answer 342N)

Relevant Equations: Fground = mg + mdg
Fn = Ffriction
Torque = Fn(d3) -mg(d2) - m2g(d1)

I set up all my summations and ended with Fnormal = ((mg1d1) + (m2gd2)) / d3. The values I put in were ((400 x 2) + (100 x 5cos60)) / 10sin60.
I got 121.243 N as my answer but that is incorrect. What did I do wrong?

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Jan 15, 2020

haruspex

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Please define all your variables (d, d1, d2, d3, m, m2, Fn) and specify your choice of axis for torque summation.
(Fn sounds like it should be normal force, but you wrote Fn=Ffriction.)

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