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JEE Main 2022 (28 Jun, Shift 2) · Torque, Couple & Equilibrium of Rigid Bodies

Torque, Couple & Equilibrium of Rigid Bodies question from JEE Main 2022 (28 Jun, Shift 2)

Q21JEE Main 2022 · 28 JUN · SHIFT 2Medium

Torque, Couple & Equilibrium of Rigid Bodies

A 34\sqrt{34} m long ladder weighing 10 kg leans on a frictionless wall. Its feet rest on the floor 3 m away from the wall as shown in the figure. If Ff and Fw are the reaction forces of the floor and the wall, then ratio of Fw/FfF_w/F_f will be:

(Use g = 10 m/s2.)

Figure

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Answer: (c)

  1. Height of the top =34−9=5= \sqrt{34 - 9} = 5 m. The smooth wall gives only a horizontal force FwF_w.
  2. Moments about the foot: Fw×5=mg×1.5=100×1.5⇒Fw=30F_w \times 5 = mg \times 1.5 = 100 \times 1.5 \Rightarrow F_w = 30 N
  3. Floor: normal =100= 100 N, friction =Fw=30= F_w = 30 N, so Ff=1002+302=10109F_f = \sqrt{100^2 + 30^2} = 10\sqrt{109} N
  4. FwFf=3010109=3109\frac{F_w}{F_f} = \frac{30}{10\sqrt{109}} = \frac{3}{\sqrt{109}}
  5. So the answer is (c) 3109\frac{3}{\sqrt{109}}.
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