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Ch 15: Oscillations
Knight Calc - Physics for Scientists and Engineers 5th Edition
Knight Calc5th EditionPhysics for Scientists and EngineersISBN: 9780137344796Not the one you use?Change textbook
Chapter 15, Problem 79

A spring is standing upright on a table with its bottom end fastened to the table. A block is dropped from a height 3.0 cm above the top of the spring. The block sticks to the top end of the spring and then oscillates with an amplitude of 10 cm. What is the oscillation frequency?

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1
Identify the key parameters of the problem: The amplitude of oscillation is 10 cm (0.1 m), and the block is dropped from a height of 3.0 cm (0.03 m) above the spring. The goal is to find the oscillation frequency, which depends on the spring constant and the mass of the block.
Use the relationship between the angular frequency \( \omega \) and the oscillation frequency \( f \): \( \omega = 2 \pi f \). The angular frequency is also related to the spring constant \( k \) and the mass \( m \) by \( \omega = \sqrt{\frac{k}{m}} \). Rearrange this to express \( f \): \( f = \frac{1}{2 \pi} \sqrt{\frac{k}{m}} \).
Determine the spring constant \( k \) using energy conservation. The block's potential energy when dropped (\( m g h \)) is converted into the spring's elastic potential energy (\( \frac{1}{2} k A^2 \)) at maximum compression. Set \( m g h = \frac{1}{2} k A^2 \) and solve for \( k \): \( k = \frac{2 m g h}{A^2} \).
Substitute \( k \) into the frequency formula. Replace \( k \) with \( \frac{2 m g h}{A^2} \) in \( f = \frac{1}{2 \pi} \sqrt{\frac{k}{m}} \). This gives \( f = \frac{1}{2 \pi} \sqrt{\frac{2 g h}{A^2}} \).
Substitute the known values: \( g = 9.8 \ \text{m/s}^2 \), \( h = 0.03 \ \text{m} \), and \( A = 0.1 \ \text{m} \). Simplify the expression to find the oscillation frequency \( f \).

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Simple Harmonic Motion (SHM)

Simple Harmonic Motion is a type of periodic motion where an object oscillates around an equilibrium position. In this case, the block attached to the spring will move back and forth due to the restoring force exerted by the spring, which is proportional to the displacement from the equilibrium position. The motion is characterized by a constant frequency and amplitude.
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Spring Constant (k)

The spring constant, denoted as 'k', is a measure of a spring's stiffness. It is defined by Hooke's Law, which states that the force exerted by a spring is directly proportional to its displacement from the equilibrium position (F = -kx). The value of 'k' is crucial for determining the frequency of oscillation in a mass-spring system.
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Frequency of Oscillation

The frequency of oscillation refers to how many complete cycles of motion occur in a unit of time, typically measured in Hertz (Hz). For a mass-spring system undergoing SHM, the frequency can be calculated using the formula f = (1/2π)√(k/m), where 'm' is the mass of the block and 'k' is the spring constant. This relationship shows how the mass and spring constant influence the oscillation rate.
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Related Practice
Textbook Question

The greenhouse-gas carbon dioxide molecule CO₂ strongly absorbs infrared radiation when its vibrational normal modes are excited by light at the normal-mode frequencies. CO₂ is a linear triatomic molecule, as shown in FIGURE CP15.82, with oxygen atoms of mass mo bonded to a central carbon atom of mass mc. You know from chemistry that the atomic masses of carbon and oxygen are, respectively, 12 and 16. Assume that the bond is an ideal spring with spring constant k. There are two normal modes of this system for which oscillations take place along the axis. (You can ignore additional bending modes.) In this problem, you will find the normal modes and then use experimental data to determine the bond spring constant. The symmetric stretch frequency is known to be 4.00 X 10¹³ Hz. What is the spring constant of the C - O bond? Use 1 u = 1 atomic mass unit = 1.66 X 10⁻²⁷ kg to find the atomic masses in SI units. Interestingly, the spring constant is similar to that of springs you might use in the lab.

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Textbook Question

The greenhouse-gas carbon dioxide molecule CO₂ strongly absorbs infrared radiation when its vibrational normal modes are excited by light at the normal-mode frequencies. CO₂ is a linear triatomic molecule, as shown in FIGURE CP15.82, with oxygen atoms of mass mo bonded to a central carbon atom of mass mc. You know from chemistry that the atomic masses of carbon and oxygen are, respectively, 12 and 16. Assume that the bond is an ideal spring with spring constant k. There are two normal modes of this system for which oscillations take place along the axis. (You can ignore additional bending modes.) In this problem, you will find the normal modes and then use experimental data to determine the bond spring constant. Use the frequency of the symmetric stretch to predict the frequency of the antisymmetric stretch. The measured frequency is 7.05 × 1013 Hz so your prediction is close but not perfect. The reason is that the bonds are not ideal springs but have a slight amount of anharmonicity. Nonetheless, you’ve learned a great deal about the CO₂ molecule from a simple model of oscillating masses.

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Textbook Question

A uniform rod of length L oscillates as a pendulum about a pivot that is a distance x from the center. For what value of x, in terms of L, is the oscillation period a minimum?

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Textbook Question

Suppose a large spherical object, such as a planet, with radius R and mass M has a narrow tunnel passing diametrically through it. A particle of mass m is inside the tunnel at a distance 𝓍 ≤ R from the center. It can be shown that the net gravitational force on the particle is due entirely to the sphere of mass with radius 𝓇 ≤ 𝓍 there is no net gravitational force from the mass in the spherical shell with 𝓇 > 𝓍. a. Find an expression for the gravitational force on the particle, assuming the object has uniform density. Your expression will be in terms of x, R, m, M, and any necessary constants.

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Textbook Question

A block on a frictionless table is connected as shown in FIGURE P15.75 to two springs having spring constants k₁ and k₂. Find an expression for the block’s oscillation frequency f in terms of the frequencies f₁ and f₂ at which it would oscillate if attached to spring 1 or spring 2 alone.

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