(III) By direct substitution, show that Eq. 14–22, with Eqs. 14–23 and 14–24, is a solution of the equation of motion (Eq. 14–21) for the forced oscillator. [Hint: To find sin ∅ and cos ∅ from tan ∅, draw a right triangle.]
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Energy in Pendulums
Problem 60a
Textbook Question
(II) A 0.735-kg block oscillates on the end of a spring whose spring constant is k = 41.0 N/m. The mass moves in a fluid which offers a resistive force F = - bv, where b = 0.662 N s/m. What is the period of the motion?

1
Step 1: Identify the type of motion described in the problem. The block is undergoing damped harmonic motion due to the resistive force F = -bv, where b is the damping coefficient. The period of damped harmonic motion is slightly modified compared to simple harmonic motion.
Step 2: Write the formula for the angular frequency of damped harmonic motion. The angular frequency is given by: , where is the natural angular frequency and is the damping coefficient divided by twice the mass.
Step 3: Calculate the natural angular frequency using the formula: , where k is the spring constant and m is the mass of the block. Substitute k = 41.0 N/m and m = 0.735 kg into the formula.
Step 4: Determine the damping coefficient using the formula: , where b is the damping constant and m is the mass. Substitute b = 0.662 N·s/m and m = 0.735 kg into the formula.
Step 5: Calculate the period of the damped motion using the relationship between angular frequency and period: . Use the values of obtained from Step 2 to find the period.

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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. The motion is characterized by a restoring force proportional to the displacement from the equilibrium, typically described by Hooke's Law for springs. The period of SHM depends on the mass of the object and the spring constant, given by the formula T = 2π√(m/k).
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Damping
Damping refers to the effect of a resistive force that reduces the amplitude of oscillations over time. In this scenario, the fluid exerts a damping force proportional to the velocity of the block, described by F = -bv. Damping affects the period of oscillation, particularly in systems where the damping is significant, leading to a modified period compared to undamped motion.
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Resonance
Resonance occurs when a system is driven at its natural frequency, leading to large amplitude oscillations. While not directly asked in this question, understanding resonance is important in the context of oscillatory systems, as it highlights the relationship between the driving frequency and the system's natural frequency. In damped systems, resonance can be affected by the damping factor, altering the peak response.
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