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Ch. 6 - Applications of Integration
Briggs - Calculus: Early Transcendentals 3rd Edition
Briggs3rd EditionCalculus: Early TranscendentalsISBN: 9780136847243Non è quello che usi tu?Cambia libro di testo
Capitolo 6, Problema 6.7.31a

Winding a chain A 30-m-long chain hangs vertically from a cylinder attached to a winch. Assume there is no friction in the system and the chain has a density of 5kg/m.
a. How much work is required to wind the entire chain onto the cylinder using the winch?

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1
Identify the physical quantities involved: the length of the chain \(L = 30\) m, the linear density \(\rho = 5\) kg/m, and gravitational acceleration \(g = 9.8\) m/s² (assuming standard gravity).
Express the mass of a small segment of the chain of length \(dx\) at a distance \(x\) from the bottom as \(dm = \rho \\ dx\), where \(x\) measures the length of chain lifted from the bottom upwards.
Determine the work required to lift this small segment \(dm\) by a height \(x\) (since the chain is being wound up from the bottom, each segment must be lifted a distance equal to its position \(x\)). The infinitesimal work is \(dW = (dm)(g)(x) = \rho g x \\ dx\).
Set up the integral for the total work by integrating \(dW\) over the entire length of the chain from \(x=0\) (bottom) to \(x=L=30\) m: \(W = \int_0^{30} \rho g x \\ dx\).
Evaluate the integral to find the total work done in winding the entire chain onto the cylinder.

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Work Done by a Variable Force

Work is the integral of force over distance. When the force varies with position, such as lifting different parts of a chain, we calculate work by integrating the force function over the displacement. This approach accounts for the changing weight as the chain is wound up.
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Work Done On A Spring (Hooke's Law)

Linear Density and Weight Calculation

Linear density is the mass per unit length of an object, here given as 5 kg/m. Multiplying linear density by gravitational acceleration and length gives the weight of a segment of the chain. This helps determine the force needed to lift varying lengths of the chain.
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Setting up and Evaluating Definite Integrals

To find total work, we set up a definite integral representing the sum of infinitesimal work elements over the chain's length. Each element corresponds to lifting a small segment of the chain a certain distance. Evaluating this integral yields the total work required.
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Definition of the Definite Integral
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