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Question

A particle executes linear simple harmonic motion with an amplitude of 2 cm. when the particle is at 1 cm from the mean position, the magnitude of the velocity and the acceleration are equal. Then its item period (in seconds) is

This question was previously asked in
NDA I 2016 GAT Previous Year Paper (17-Apr-2016)
The correct answer is \(\frac{{2\pi }}{{\sqrt 3 }}\;\)

Understanding Simple Harmonic Motion (SHM)

Simple Harmonic Motion (SHM) is a special type of periodic motion where the restoring force is directly proportional to the displacement from the mean position and acts towards the mean position. We are given a particle executing linear SHM.

Analyzing the Given SHM Problem

We are provided with the following information for the particle's motion:

  • Amplitude of the SHM, \(A = 2\) cm.
  • Position of the particle from the mean position, \(x = 1\) cm.
  • At this specific position (\(x = 1\) cm), the magnitude of the particle's velocity is equal to the magnitude of its acceleration. That is, \(|v| = |a|\).

We need to find the time period (\(T\)) of the oscillation in seconds.

Formulas for Velocity and Acceleration in SHM

For a particle executing SHM, the velocity (\(v\)) and acceleration (\(a\)) at a displacement \(x\) from the mean position are given by:

  • Velocity: \(v = \pm \omega \sqrt{A^2 - x^2}\), where \(\omega\) is the angular frequency.
  • Acceleration: \(a = -\omega^2 x\), where \(\omega\) is the angular frequency.

Setting up the Equation from the Given Condition

The problem states that the magnitude of velocity equals the magnitude of acceleration when \(x = 1\) cm.

\(|v| = |a|\)

Using the formulas:

\(|\pm \omega \sqrt{A^2 - x^2}| = |-\omega^2 x|\)

Taking magnitudes, and knowing \(\omega\) is a positive value for oscillations and \(x=1\) cm is a positive displacement:

\(\omega \sqrt{A^2 - x^2} = \omega^2 x\)

Solving for Angular Frequency (\(\omega\))

Now, we substitute the given values \(A = 2\) cm and \(x = 1\) cm into the equation:

\(\omega \sqrt{(2)^2 - (1)^2} = \omega^2 (1)\)

\(\omega \sqrt{4 - 1} = \omega^2\)

\(\omega \sqrt{3} = \omega^2\)

Since the particle is oscillating, \(\omega\) cannot be zero. We can divide both sides by \(\omega\):

\(\sqrt{3} = \omega\)

So, the angular frequency is \(\omega = \sqrt{3}\) rad/s.

Calculating the Time Period (T) of SHM

The relationship between angular frequency (\(\omega\)) and time period (\(T\)) is given by:

\(T = \frac{2\pi}{\omega}\)

Substituting the value of \(\omega = \sqrt{3}\):

\(T = \frac{2\pi}{\sqrt{3}}\) seconds

Conclusion

The time period of the particle executing simple harmonic motion is \(\frac{2\pi}{\sqrt{3}}\) seconds.

Given Information Value
Amplitude (A) 2 cm
Position (x) 1 cm
Condition \(|v| = |a|\) at \(x=1\) cm
Derived Value Value
Angular Frequency (\(\omega\)) \(\sqrt{3}\) rad/s
Time Period (T) \(\frac{2\pi}{\sqrt{3}}\) s

SHM Problem Revision Table

Let's quickly review the key formulas used in this SHM problem.

Concept Formula
Velocity (v) at position x \(v = \pm \omega \sqrt{A^2 - x^2}\)
Acceleration (a) at position x \(a = -\omega^2 x\)
Relationship between T and \(\omega\) \(T = \frac{2\pi}{\omega}\)

Additional Information on Simple Harmonic Motion

Simple Harmonic Motion is a fundamental concept in physics, describing oscillations. Here's a bit more detail:

  • Mean Position: This is the equilibrium position where the net force on the particle is zero. Displacement (x) is measured from this position.
  • Amplitude (A): The maximum displacement of the particle from its mean position.
  • Angular Frequency (\(\omega\)): Represents how fast the oscillation is occurring, related to the properties of the system (like mass and spring constant for a mass-spring system). Units are typically radians per second.
  • Time Period (T): The time taken for one complete oscillation (or cycle).
  • Frequency (f): The number of oscillations per unit time. \(f = 1/T = \omega / (2\pi)\).
  • Relationship between v, a, x, A, \(\omega\): The formulas used in the solution (\(v = \pm \omega \sqrt{A^2 - x^2}\) and \(a = -\omega^2 x\)) are derived from the basic differential equation of SHM, \(\frac{d^2x}{dt^2} = -\omega^2 x\).

Understanding these fundamental concepts is crucial for solving problems related to SHM, including those involving velocity, acceleration, amplitude, and time period.

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Important Questions from Simple Harmonic Motion

  1. A particle is executing SHM of amplitude 9 and time period of 4 seconds, then the time taken by it to move from the extreme position to half the amplitude is

  2. A particle performs simple harmonic motion, where its displacement is described by $x(t) = A \cos(\omega t + \phi)$. If the particle's oscillation frequency is $f$, what is the frequency with which its kinetic energy oscillates?
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  4. The sound from the bee is produced when its wings vibrates at 360 vibrations per second. The Time Period of the vibration would be

  5. When a mass is hung from the lower of a spring of negligible mass, an extension x is produced in spring. The mass is set into vertical oscillations. The time period of oscillation is:

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