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Simple Pendulum question from JEE Main 2015

Q77JEE Main 2015Medium

Simple Pendulum

The period of oscillation of a simple pendulum is T=2πLgT = 2\pi\sqrt{\frac{L}{g}}. Measured value of L is 20.0 cm known to 1 mm accuracy and time for 100 oscillations of the pendulum is found to be 90 s using wrist watch of 1 s resolution. The accuracy in the determination of g is:

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Answer: (d)

  1. Δgg=ΔLL+2Δtt\frac{\Delta g}{g} = \frac{\Delta L}{L} + 2\frac{\Delta t}{t}.
  2. ΔLL=0.120.0=0.5%\frac{\Delta L}{L} = \frac{0.1}{20.0} = 0.5\%; 2Δtt=2×190≈2.2%2\frac{\Delta t}{t} = 2 \times \frac{1}{90} \approx 2.2\%.
  3. Total ≈2.7%≈3%\approx 2.7\% \approx 3\%.
  4. So the answer is (d) 3%3\%.
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