2. A 20-foot chain with density 4 lb/ft hangs off the roof of a building. How much work is required to pull the chain to the roof?

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**Work Calculation for Lifting a Chain**

**Problem:**

A 20-foot chain with a density of 4 lb/ft hangs off the roof of a building. How much work is required to pull the chain to the roof?

**Explanation:**

Consider the given problem: we have a uniform chain hanging from a building, and we need to calculate the work required to pull the entire chain to the roof.

### Given Data:

- Length of the chain: 20 feet
- Density of the chain: 4 pounds per foot (lb/ft)

### Steps to Solve:

1. **Determine the Force:**
   
   The force required is based on the weight of the chain per foot. Since the chain's density is uniform:
   \[
   \text{Weight per unit length} = 4 \text{ lb/ft}
   \]

2. **Set Up the Work Integral:**
   
   Work (\(W\)) is defined as the integral of force (\(F\)) times distance (\(d\)):
   \[
   W = \int_{0}^{L} F(x) \, dx
   \]
   
   Where \(L\) is the length of the chain (20 feet) and \(x\) represents an incremental length of the chain being lifted.

3. **Integrate the Force over the Distance:**
   
   Since the weight is linearly distributed, let \(x\) be the distance from the bottom of the chain:
   \[
   F(x) = 4 \, \text{lb/ft} \times (20 - x) \, \text{feet}
   \]
   
   The integral becomes:
   \[
   W = \int_{0}^{20} 4 \times (20 - x) \, dx
   \]

4. **Calculate the Integral:**

   Break down the calculation:
   \[
   W = 4 \int_{0}^{20} (20 - x) \, dx
   \]
   
   Perform the integral:
   \[
   W = 4 \left[ 20x - \frac{x^2}{2} \right]_{0}^{20}
   \]
   
   Evaluate the integral at the bounds:
   \[
   W = 4 \left[ (20 \times 20) - \frac{20^2}{2} \right]
   \]
Transcribed Image Text:**Work Calculation for Lifting a Chain** **Problem:** A 20-foot chain with a density of 4 lb/ft hangs off the roof of a building. How much work is required to pull the chain to the roof? **Explanation:** Consider the given problem: we have a uniform chain hanging from a building, and we need to calculate the work required to pull the entire chain to the roof. ### Given Data: - Length of the chain: 20 feet - Density of the chain: 4 pounds per foot (lb/ft) ### Steps to Solve: 1. **Determine the Force:** The force required is based on the weight of the chain per foot. Since the chain's density is uniform: \[ \text{Weight per unit length} = 4 \text{ lb/ft} \] 2. **Set Up the Work Integral:** Work (\(W\)) is defined as the integral of force (\(F\)) times distance (\(d\)): \[ W = \int_{0}^{L} F(x) \, dx \] Where \(L\) is the length of the chain (20 feet) and \(x\) represents an incremental length of the chain being lifted. 3. **Integrate the Force over the Distance:** Since the weight is linearly distributed, let \(x\) be the distance from the bottom of the chain: \[ F(x) = 4 \, \text{lb/ft} \times (20 - x) \, \text{feet} \] The integral becomes: \[ W = \int_{0}^{20} 4 \times (20 - x) \, dx \] 4. **Calculate the Integral:** Break down the calculation: \[ W = 4 \int_{0}^{20} (20 - x) \, dx \] Perform the integral: \[ W = 4 \left[ 20x - \frac{x^2}{2} \right]_{0}^{20} \] Evaluate the integral at the bounds: \[ W = 4 \left[ (20 \times 20) - \frac{20^2}{2} \right] \]
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