Two identical, thin rods, each with mass m and length L, are joined at right angles to form an L-shaped object. This object is balanced on top of a sharp edge. If the L-shaped object is deflected slightly, it oscillates.


Find the frequency of oscillation.

Verified Answer :

The frequency of oscillation of the given L-shaped object made of two rods is \(\boxed{\frac{1}{{2\pi }}\sqrt{\frac{{3g}}{{4\sqrt2L}}}}\) .


Further Explanation:


The combination of the two rods perpendicular to each other and making a L-shaped object is as shown in figure attached below.


This L-shaped object rests on a sharp edge and therefore, each rod will make an angle of \(45^\circ\)  with the sharp edge. When there is a very small deflection in the rod, it will start performing oscillations with a small angle \(\theta\) . Then the time period of oscillation of this rod about its center of gravity is given as:

\(T=2\pi \sqrt {\frac{I}{{mgd}}}\)                                       …… (1)

Here, \(I\)  is the moment of inertia of the rod, \(d\)  is the distance of the center of gravity from the fixed point and \(T\)  is the time period of oscillation of the L-shaped object.


The moment of inertia of the rod about its one end is given as:

\(I=\frac{1}{3}M{L^2}\)

For the above mentioned case, the moment of inertia of the two rods about the fixed sharp point is:

\(\begin{aligned}I&=\frac{1}{3}m{L^2}+\frac{1}{3}m{L^2}\\&=\frac{2}{3}m{L^2}\\\end{aligned}\)

The distance of the center of gravity from the fixed point is:

\(d=\frac{L}{{2\sqrt 2 }}\)

Substitute the values in equation (1).

\(\begin{aligned}T&=2\pi\sqrt{\frac{{\frac{2}{3}m{L^2}}}{{mg\left({\frac{L}{{2\sqrt 2 }}}\right)}}}\\&=2\pi\sqrt{\frac{{4\sqrt 2 L}}{{3g}}}\\\end{aligned}\)

The frequency of oscillation of the L-shaped object is:

\(\begin{aligned}f&=\frac{1}{T}\\&=\frac{1}{{2\pi}}\sqrt{\frac{{3g}}{{4\sqrt 2 L}}}\\\end{aligned}\)

Thus, the frequency of oscillation of the given L-shaped object made of two rods is

\(\boxed{\frac{1}{{2\pi }}\sqrt{\frac{{3g}}{{4\sqrt 2 L}}}}\) .

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Answer Details:

Grade: Senior School

Subject: Physics

Chapter: Simple Harmonic Motion


Keywords:

L-shaped object, two identical thin rods, balanced, a sharp edge, deflected slightly, moment of inertia, frequency of oscillation, center of gravity.

View image snehapa

The amount of time in which an action or a state continues to exist. Due to the nature of the activity or situation under examination, it can be measured in seconds or millions of years. so, the calculted time is "\(\bold{2\pi \sqrt{\frac{\sqrt{2}L}{3g}}}\)" .

Time period calculation:

The rod has a mass of m.

L is the length of a single rod.

If it's connecting at \(\bold{90^{\circ}}\), as per the query,

Following that the combined system's moment of inertia.

\(\to \frac{mL^2}{3} + \frac{mL^2}{3}=\frac{2mL^2}{3}\)

The pendulum's effective length:

\(\to L \cos 45^{\circ}= L \times \frac{1}{\sqrt{2}} =\frac{L}{\sqrt{2}}\\\\\)

Calculating the time period:

\(T =2\pi \sqrt{\frac{I}{mgl}} \\\\\)

   \(= 2\pi \sqrt{\frac{2\times mL^2 \times \sqrt{2}}{3 \times 2 mgL}}\\\\\)

   \(= 2\pi \sqrt{\frac{L\sqrt{2}}{3 \times g}} \\\\= 2\pi \sqrt{\frac{\sqrt{2}L}{3g}}\)

Find out more about the time period here:

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