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JEE Main 202228 JuneEvening Shift
Exam
JEE Main
Year
2022
Date
28 June
Shift
Evening Shift
Subject
Physics
Chapter
Rotational Motion

JEE Main 2022 · 28 June · Evening Shift · Physics · Rotational Motion

A 34 m long ladder weighing 10kg leans on a frictionless wall. Its...

A 34m\sqrt{34}m long ladder weighing 10kg10kg leans on a frictionless wall. Its feet rest on the floor 3m3m away from the wall as shown in the figure. If Ff{F}_{f} and Fw{F}_{w} are the reaction forces of the floor and the wall, then ratio of FwFf\dfrac{{F}_{w}}{{F}_{f}} will be :
(Use g=10ms−2g = 10m{s}^{- 2}.)

A 34 m long ladder weighing 10kg leans on a frictionless wall. Its feet rest on the floor 3m away from the wall as

Options

  1. A6110\dfrac{6}{\sqrt{110}}
  2. B3113\dfrac{3}{\sqrt{113}}
  3. C3109\dfrac{3}{\sqrt{109}}
  4. D2109\dfrac{2}{\sqrt{109}}

Correct answer

C. 3109\dfrac{3}{\sqrt{109}}

Step-by-step solution

A 34 m long ladder weighing 10kg leans on a frictionless wall. Its feet rest on the floor 3m away from the wall as

Applying force balance in vertical direction

N1=mg=100N{N}_{1} = mg = 100N

Applying torque balance at the bottom contact point,

mg×32=N2×5⇒N2=Fw=30Nmg \times \dfrac{3}{2} = {N}_{2} \times 5 ⇒ {N}_{2} = {F}_{w} = 30N

Applying force balance in horizontal direction

fs=N2=30N{f}_{s} = {N}_{2} = 30N

Net reaction at the floor will be,

Ff=N12+fs2=1002+302=10109N{F}_{f} = \sqrt{{{N}_{1}}^{2} + {{f}_{s}}^{2}} = \sqrt{{100}^{2} + {30}^{2}} = 10\sqrt{109}N

Therefore, FwFf=3010109=3109\dfrac{{F}_{w}}{{F}_{f}} = \dfrac{30}{10\sqrt{109}} = \dfrac{3}{\sqrt{109}}

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