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JEE Main 2021 (20 Jul, Shift 1) · Apparent Weight & Lift

Apparent Weight & Lift question from JEE Main 2021 (20 Jul, Shift 1)

Q15JEE Main 2021 · 20 JUL · SHIFT 1Medium

Apparent Weight & Lift

A steel block of 10 kg rests on a horizontal floor as shown. When three iron cylinders are placed on it as shown, the block and cylinders go down with an acceleration 0.2 m/s2. The normal reaction R' by the floor if mass of the iron cylinders are equal and of 20 kg each, is ____________ N. [Take g = 10 m/s2 and μ\mus = 0.2]

Figure

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Answer: (a)

  1. Total mass =10+3×20=70= 10 + 3 \times 20 = 70 kg, accelerating down with a=0.2 m/s2a = 0.2\text{ m/s}^2.
  2. R′=m(g−a)=70×(10−0.2)=70×9.8R' = m(g - a) = 70 \times (10 - 0.2) = 70 \times 9.8
  3. R′=686R' = 686 N (μs\mu_s is not needed).
  4. So the answer is (a) 686.
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