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JEE Main 20154 April
Exam
JEE Main
Year
2015
Date
4 April
Subject
Physics
Chapter
Mathematics in Physics

JEE Main 2015 · 4 April · Physics · Mathematics in Physics

The period of oscillation of a simple pendulum is T = 2π (l)/(g) ....

The period of oscillation of a simple pendulum is T=2πlg.T = 2\pi\sqrt{\dfrac{l}{g}} . Measured value of ll is 20.0cm20 . 0cm, known to 1mm1mm accuracy and time for 100100oscillations of the pendulum is found to be 90s90s using a wristwatch of 1s1s resolution. The accuracy in the determination of gg is

Options

  1. A55 %
  2. B44 %
  3. C33 %
  4. D11 %

Correct answer

C. 33 %

Step-by-step solution

∴T=2πlg⇒g=4π2lT2∴ T = 2\pi\sqrt{\dfrac{l}{g}} ⇒ g = 4{\pi}^{2}\dfrac{l}{T^{2}}

∴∴ Error in~gg can be calculated as

\Deltagg=\Deltall+2ΔTT\dfrac{\Deltag}{g} = \dfrac{\Deltal}{l} + \dfrac{2\Delta T}{T}.~

∴∴ Total time for~nnoscillation is t=nTt = nT where TT= time for oscillation.

⇒\Deltatt=ΔTT⇒ \dfrac{\Deltat}{t} = \dfrac{\Delta T}{T}

⇒\Deltagg=\Deltall+2\Deltatt⇒ \dfrac{\Deltag}{g} = \dfrac{\Deltal}{l} + \dfrac{2\Deltat}{t}

Given that \Deltal=1mm=10−3m,l=20×10−2m\Deltal = 1mm = {10}^{- 3}m, l = 20 \times {10}^{- 2}m

\Deltat=1s,t=90s\Deltat = 1s, t = 90s.~

%erroring is

\Deltagg×100=(\Deltall+2\Deltatt)×100\dfrac{\Deltag}{g} \times 100 = \left(\dfrac{\Deltal}{l} + \dfrac{2\Deltat}{t}\right) \times 100

=(10−320×10−2+2×190)×100=12+209=0.5+2.22=2.72= \left(\dfrac{{10}^{- 3}}{20 \times {10}^{- 2}} + \dfrac{2 \times 1}{90}\right) \times 100= \dfrac{1}{2} + \dfrac{20}{9}= 0.5 + 2.22= 2.72%

≅3≅ 3%
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