Energy in a Spring-Mass Oscillator

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Oscillations Beginner Simple harmonic oscillation

Source: Principles of Physics

Problem

A vibrating spring-mass oscillator has a mechanical energy $E = 1.0$ J, an amplitude $A = 0.10$ m, and a maximum velocity $v_{max} = 1.0$ m/s.

  1. Find the spring constant.
  2. Find the mass of the oscillator.
  3. Find the vibration frequency.

[Q1] $k = 200$ N/m [Q2] $m = 2.0$ kg [Q3] $f = 1.59$ Hz

The total mechanical energy $E$ of an oscillator can be expressed as the maximum potential energy or the maximum kinetic energy. Maximum potential energy: $E = \frac{1}{2} k A^2$ Maximum kinetic energy: $E = \frac{1}{2} m v_{max}^2$

[Q1] The spring constant $k$ can be found from the total energy and amplitude:

$$k = \frac{2E}{A^2} = \frac{2(1.0)}{(0.10)^2} = 200 \, \text{N/m}$$

[Q2] The mass $m$ can be found from the total energy and maximum velocity:

$$m = \frac{2E}{v_{max}^2} = \frac{2(1.0)}{(1.0)^2} = 2.0 \, \text{kg}$$

[Q3] The frequency $f$ can be found from the angular frequency $\omega$. We know $v_{max} = A\omega$, so $\omega = v_{max}/A$. The frequency is $f = \omega/(2\pi)$.

$$f = \frac{v_{max}}{2\pi A} = \frac{1.0}{2\pi (0.10)} = \frac{5}{\pi} \, \text{Hz}$$