Simple Harmonic Motion 3 Question 9

9. A uniform cylinder of length L and mass M having cross-sectional area A is suspended, with its length vertical, from a fixed point by a massless spring, such that it is half-submerged in a liquid of density ρ at equilibrium position. When the cylinder is given a small downward push and released it starts oscillating vertically with a small amplitude. If the force constant of the spring is k, the frequency of oscillation of the cylinder is

(1990,2M)

(a) 12πkAρgM1/2

(b) 12πk+AρgM1/2

(c) 12πk+ρgL2M

(d) 12πk+Aρg1/2Aρg

Analytical & Descriptive Questions

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Answer:

Correct Answer: 9. (b)

Solution:

  1. When cylinder is displaced by an amount x from its mean position, spring force and upthrust both will increase. Hence,

Net restoring force = extra spring force + extra upthrust

or

F=(kx+Axρg)

or a=k+ρAgMx

Now, f=12π|ax|=12πk+ρAgM

Correct option is (b).



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