A mass weighting 24 lbs stretches a spring 2 inches. The mass is in a medium that exerts a viscous resistance of 28 lbs when the mass has a velocity of 2 ft/sec.

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Author:Raymond A. Serway, Chris Vuille
Publisher:Raymond A. Serway, Chris Vuille
Chapter1: Units, Trigonometry. And Vectors
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**Problem Statement:**

A mass weighing 24 lbs stretches a spring 2 inches. The mass is in a medium that exerts a viscous resistance of 28 lbs when the mass has a velocity of 2 ft/sec.

Suppose the object is displaced an additional 6 inches and released.

Find an equation for the object's displacement, \( u(t) \), in feet after \( t \) seconds.

\[ u(t) = \] (with a blank placeholder for the equation)

---

### Analysis and Problem-Solving Steps:

1. **Determine Constants:**
    - **Spring Constant (k):**
		The weight of the mass, \( W = 24 \) lbs, stretches the spring by 2 inches \( = \frac{2}{12} \) ft \( = \frac{1}{6} \) ft.
		Using Hooke's Law: \( W = kx \), where \( x \) is the displacement,
		\[ 24 = k \left( \frac{1}{6} \right) \]
		Solving for \( k \):
		\[ k = 24 \times 6 = 144 \text{ lbs/ft} \]

    - **Damping Coefficient (c):**
		The viscous resistance is \( 28 \) lbs at \( 2 \) ft/sec,
		\[ c \cdot 2 = 28 \]
		Solving for \( c \):
		\[ c = \frac{28}{2} = 14 \text{ lbs/(ft/sec)} \]

2. **Formulating the Differential Equation:**
    - For mass-spring-damper systems: \( m \ddot{u}(t) + c \dot{u}(t) + ku(t) = 0 \).
    - Converting the mass weight to mass \( (m) \):
	    \[ W = mg \implies 24 = m \cdot 32 \]
	    \[ m = \frac{24}{32} = \frac{3}{4} \text{ slugs} \]

    - Plugging in the values:
		\[ \frac{3}{4} \ddot{u}(t) + 14 \dot{u}(t) + 144 u(t) = 0 \]

    - Simplifying the differential equation:
Transcribed Image Text:**Problem Statement:** A mass weighing 24 lbs stretches a spring 2 inches. The mass is in a medium that exerts a viscous resistance of 28 lbs when the mass has a velocity of 2 ft/sec. Suppose the object is displaced an additional 6 inches and released. Find an equation for the object's displacement, \( u(t) \), in feet after \( t \) seconds. \[ u(t) = \] (with a blank placeholder for the equation) --- ### Analysis and Problem-Solving Steps: 1. **Determine Constants:** - **Spring Constant (k):** The weight of the mass, \( W = 24 \) lbs, stretches the spring by 2 inches \( = \frac{2}{12} \) ft \( = \frac{1}{6} \) ft. Using Hooke's Law: \( W = kx \), where \( x \) is the displacement, \[ 24 = k \left( \frac{1}{6} \right) \] Solving for \( k \): \[ k = 24 \times 6 = 144 \text{ lbs/ft} \] - **Damping Coefficient (c):** The viscous resistance is \( 28 \) lbs at \( 2 \) ft/sec, \[ c \cdot 2 = 28 \] Solving for \( c \): \[ c = \frac{28}{2} = 14 \text{ lbs/(ft/sec)} \] 2. **Formulating the Differential Equation:** - For mass-spring-damper systems: \( m \ddot{u}(t) + c \dot{u}(t) + ku(t) = 0 \). - Converting the mass weight to mass \( (m) \): \[ W = mg \implies 24 = m \cdot 32 \] \[ m = \frac{24}{32} = \frac{3}{4} \text{ slugs} \] - Plugging in the values: \[ \frac{3}{4} \ddot{u}(t) + 14 \dot{u}(t) + 144 u(t) = 0 \] - Simplifying the differential equation:
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