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JEE Main 2021 (26 Aug, Shift 2) · Errors in Measurement

Errors in Measurement question from JEE Main 2021 (26 Aug, Shift 2)

Q89JEE Main 2021 · 26 AUG · SHIFT 2Difficult

Errors in Measurement

The acceleration due to gravity is found upto an accuracy of 4% on a planet. The energy supplied to a simple pendulum of known mass 'm' to undertake oscillations of time period T is being estimated. If time period is measured to an accuracy of 3%, the accuracy to which E is known is ..............%

Numerical answer type. Work it out, then open the answer.

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Answer: 14

  1. Pendulum energy E=12mω2A2=12mgL(Lθ)2=12mgLθ2E = \tfrac{1}{2}m\omega^2A^2 = \tfrac{1}{2}m\dfrac{g}{L}(L\theta)^2 = \tfrac{1}{2}mgL\theta^2.
  2. From T=2πL/gT = 2\pi\sqrt{L/g}: L=gT24π2L = \dfrac{gT^2}{4\pi^2}, so E∝g2T2E \propto g^2T^2 (for fixed mm, θ\theta).
  3. ΔEE=2Δgg+2ΔTT=2(4)+2(3)\dfrac{\Delta E}{E} = 2\dfrac{\Delta g}{g} + 2\dfrac{\Delta T}{T} = 2(4) + 2(3)
  4. =14%= 14\%
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