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JEE Main 2020 (8 Jan, Shift 1) · Archimedes' Principle & Floatation

Archimedes' Principle & Floatation question from JEE Main 2020 (8 Jan, Shift 1)

Q16JEE Main 2020 · 8 JAN · SHIFT 1Medium

Archimedes' Principle & Floatation

A leak proof cylinder of length 1m, made of a metal which has very low coefficient of expansion is floating vertically in water at 0°C such that its height above the water surface is 20 cm. When the temperature of water is increased to 4°C, the height of the cylinder above the water surface becomes 21 cm. The density of water at T = 4°C, relative to the density at T = 0°C is close to:

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Answer: (c)

  1. Weight is constant, so ρ hsub\rho\,h_{sub} = constant (same cross-section).
  2. Submerged length: 100−20=80100 - 20 = 80 cm at 0∘0^\circC, 100−21=79100 - 21 = 79 cm at 4∘4^\circC.
  3. ρ0×80=ρ4×79⇒ρ4ρ0=8079≈1.013\rho_0 \times 80 = \rho_4 \times 79 \Rightarrow \dfrac{\rho_4}{\rho_0} = \dfrac{80}{79} \approx 1.013
  4. So the answer is (c) 1.01.
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