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13.Oscillations
medium
A simple pendulum with a metallic bob has a time period $T$. The bob is now immersed in a non-viscous liquid and oscillated. If the density of the liquid is $1 / 4$ that of metal, the time period of the same pendulum will be ...........
A
$\frac{T}{\sqrt{3}}$
B
$\frac{2 T}{\sqrt{3}}$
C
$\frac{4}{3} T$
D
$\frac{2}{3} T$
Solution
(b)
Normal time period $T=2 \pi \sqrt{\frac{l}{g}}$
When immersed in a liquid. It experiences an upthrust.
Upthrust $=\frac{\rho}{4} \times$ volume $g$
Upward acceleration $=$ Upward force $/$ mass of ball $=\frac{g}{4}$
$T^{\prime}=2 \pi \sqrt{\frac{I}{g_{e f f}}}$
$g_{\text {eff }}=g-\frac{g}{4}=\frac{3}{4} g$
$T^{\prime}=2 \pi=\sqrt{\frac{1}{3 g} \times 4}=\frac{2 T}{\sqrt{3}}$
Standard 11
Physics