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A mass is suspended on a spring. The spring is compressed so that the mass is located 5 cm above its rest position. The mass is released at time \(t=0\) and allowed to oscillate. It is observed that the mass reaches its lowest point \(\frac{1}{2} \mathrm{s}\) after it is released. Find an equation that describes the motion of the mass.

Short Answer

Expert verified
The equation of motion for the mass is \( x(t) = 5 \cos(2\pi t) \).

Step by step solution

01

Understand the Motion

The mass-spring system exhibits simple harmonic motion (SHM) with the equilibrium position being the rest position of the spring. The motion starts 5 cm above this equilibrium position and reaches its lowest point after 0.5 seconds.
02

Identify Key Values

From the problem, we know: 1. The amplitude, \( A \), is 5 cm (the maximum displacement from the equilibrium position). 2. The time for one full oscillation cycle, known as the period \( T \), can be deduced since it takes 0.5 seconds to go from the highest point to the lowest point. Hence, the full cycle takes 1 second.
03

Equation of Motion

The general equation for simple harmonic motion is of the form: \[ x(t) = A \cos(\omega t + \phi) \] where \( \omega = \frac{2\pi}{T} \) is the angular frequency and \( \phi \) is the phase constant.
04

Calculate Angular Frequency

Given the period \( T = 1 \) second, the angular frequency \( \omega \) is calculated as: \[ \omega = \frac{2\pi}{T} = 2\pi \text{ radians/second} \]
05

Determine the Phase Constant

Since the motion starts at 5 cm above the equilibrium position when \( t = 0 \), \( x(0) = A \). Thus, \( \phi = 0 \) because \( \cos(0) = 1 \).
06

Write the Complete Equation of Motion

Substituting the known values into the formula, the equation of motion becomes: \[ x(t) = 5 \cos(2\pi t) \] where \( A = 5 \), \( \omega = 2\pi \), and \( \phi = 0 \).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Mass-Spring System
A mass-spring system is a classic example in physics illustrating simple harmonic motion (SHM). This system consists of a mass that is attached to a spring, which can compress or extend. The mass experiences a force exerted by the spring, which aims to restore the mass to the spring's equilibrium position. The equilibrium position is the point at which the net force on the mass is zero, and the spring is neither compressed nor stretched. In the exercise, the system starts with the mass 5 cm above the equilibrium position. This setup is crucial because it initiates oscillation, which is a repetitive back-and-forth motion around the equilibrium point. It helps us understand how forces work to restore balance and how the mass's energy changes between potential and kinetic energy over time.
Oscillation
Oscillation refers to the regular and repetitive back-and-forth or up-and-down motion performed by an object around a central point. In a mass-spring system, oscillation is seen as the mass travels back and forth over the same path, crossing its equilibrium position just like a pendulum or seesaw. The mass moves fastest as it passes through the equilibrium position and slows down as it reaches its maximum displacement, known as the amplitude. Characteristics of oscillation include a complete cycle, which is from the highest point, through the lowest point, and back again. The speed and behavior of this motion are influenced by factors such as mass and spring stiffness. Understanding oscillation aids in grasping complex wave behaviors and energy transfer concepts in physics. For this exercise, oscillation time is crucial since it informs us about the periodic nature of the motion described by the equation.
Angular Frequency
Angular frequency (\( \omega \)) is a critical parameter in the description of oscillatory motions such as those in a mass-spring system. It represents how fast the oscillation cycles are completed and is measured in radians per second. The formula for angular frequency is:\[ \omega = \frac{2\pi}{T} \]where\( T \)is the period of one complete cycle. In the given problem, since it takes 1 second for the mass to complete a full cycle, the angular frequency is\( 2\pi \, \text{radians/second} \).
  • Significance: The larger the angular frequency, the faster the system oscillates.
  • Application in Equations: It is used in the equation of motion for simple harmonic oscillators to determine the precise motion path.
Understanding angular frequency helps in predicting and calibrating the behavior of oscillating systems and connecting periodic time scales with oscillatory behavior.
Amplitude
Amplitude in oscillatory motion, such as in a mass-spring system, describes the maximum displacement from the equilibrium position. It is a measure of how far the mass moves from its resting state, both upward and downward, during each oscillation cycle. For this problem, the mass starts 5 cm above its rest position, which defines the amplitude as 5 cm. Amplitude provides insights into the energy of the oscillating system. Larger amplitudes mean the system has more energy, since the energy in an oscillating system is largely determined by its maximum displacement. Knowing amplitude is essential for writing the equation of motion as it tells us how far from the equilibrium the motion starts.

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Most popular questions from this chapter

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The frequency of oscillation of an object suspended on a spring depends on the stiffness \(k\) of the spring (called the spring constant) and the mass \(m\) of the object. If the spring is compressed a distance \(a\) and then allowed to oscillate, its displacement is given by $$f(t)=a \cos \sqrt{k / m} t$$ (a) A 10 -g mass is suspended from a spring with stiffness \(k=3 .\) If the spring is compressed a distance 5 cm and then released, find the equation that describes the oscillation of the spring. (b) Find a general formula for the frequency (in terms of \(k\) and \(m\) ). (c) How is the frequency affected if the mass is increased? Is the oscillation faster or slower? (d) How is the frequency affected if a stiffer spring is used (larger \(k\) )? Is the oscillation faster or slower?

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