Oscillations

JEE Main level, single correct, medium

132 of 194

Question 132 of 194

A cylindrical plastic bottle of negligible mass is filled with 310ml310 ml of water and left floating in a pond with still water. If pressed downward slightly and released, it starts performing simple harmonic motion at angular frequency ω.\omega . If the radius of the bottle is 2.5cm2.5 cm then ω\omega is close to: (( density of water =103kg/m3)={10}^{3}kg/{m}^{3})

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Answer: (C) 7.9radsec−1⁡{7.9 rad sec}^{-1}⁡

Let at equilibrium, yy length of bottle is immerged in water:

So,
mg=fbuomg={f}_{buo}

mg=ρ(Ay)gmg=\rho \left(Ay\right)g ..... (1)(1) [Equilibrium Condition]

Now it is further pushed by distance
xx

Frestoring=ρ[A(x+y)]g−mg{F}_{restoring}=\rho [A\left(x+y)\right]g-mg

mω2x=ρAxg+ρAyg−mgm{\omega }^{2}x=\rho Axg+\rho Ayg-mg

ω=ρAgm=ρAgρV=πr2gV=7.9rad/sec\omega =\sqrt{\dfrac{\rho Ag}{m}}=\sqrt{\dfrac{\rho Ag}{\rho V}}=\sqrt{\dfrac{\pi {r}^{2}g}{V}}=7.9rad/sec

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