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Ch. 7 - Logarithmic, Exponential Functions, and Hyperbolic Functions
Briggs - Calculus: Early Transcendentals 3rd Edition
Briggs3rd EditionCalculus: Early TranscendentalsISBN: 9780136847243Non è quello che usi tu?Cambia libro di testo
Capitolo 7, Problema 7.2.44b

A running model A model for the startup of a runner in a short race results in the velocity function v(t) = a(1 - e⁻ᵗ/ᶜ), where a and c are positive constants, t is measured in seconds, and v has units of m/s. (Source: Joe Keller, A Theory of Competitive Running, Physics Today, 26, Sep 1973)


b. Using the velocity in part (a) and assuming s(0) = 0, find the position function s(t), for t ≥ 0.

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Recall that the position function \(s(t)\) is the integral of the velocity function \(v(t)\) with respect to time \(t\). Mathematically, this is expressed as \(s(t) = \int v(t) \, dt + C\), where \(C\) is the constant of integration.
Substitute the given velocity function \(v(t) = a(1 - e^{-t/c})\) into the integral to get \(s(t) = \int a(1 - e^{-t/c}) \, dt + C\).
Split the integral into two parts: \(s(t) = a \int 1 \, dt - a \int e^{-t/c} \, dt + C\).
Integrate each term separately: the integral of 1 with respect to \(t\) is \(t\), and the integral of \(e^{-t/c}\) with respect to \(t\) involves using the substitution \(u = -t/c\), so \(\int e^{-t/c} \, dt = -c e^{-t/c} + D\), where \(D\) is another constant of integration.
Combine the results to write \(s(t) = a \left( t + c e^{-t/c} \right) + C\). Use the initial condition \(s(0) = 0\) to solve for \(C\) by substituting \(t=0\) into the expression and setting \(s(0) = 0\).

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Velocity and Position Relationship

Velocity is the rate of change of position with respect to time. Mathematically, velocity v(t) is the derivative of position s(t), so s(t) can be found by integrating v(t) over time. Given an initial position, integrating the velocity function yields the position function.
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Initial conditions, such as s(0) = 0, are used to determine the constant of integration after integrating a velocity function. They ensure the position function accurately reflects the physical scenario, anchoring the solution to a specific starting point.
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