For a fish swimming at a speed v relative to the water, the energy expenditure per unit time is proportional to v3. It is believed that migrating fish try to minimize the total energy required to swim a fixed distance. If the fish are swimming against a current u (u < v), then the time required to swim a distance L is L/(v-u) and the total energy E required to swim the distance is given by the formula below, where a is the proportionality constant.E(v) = av^3 L/(v - u)1. Determine the value of v that minimizes E.

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Answer:

Value of v that minimizes E is v = 3u/2

Step-by-step explanation:

We are given that;

E(v) = av³L/(v-u)

Now, using the quotient rule, we have;

dE/dv = [(v-u)•3av²L - av³L(1)]/(v - u)²

Expanding and equating to zero, we have;

[3av³L - 3av²uL - av³L]/(v - u)² = 0

This gives;

(2av³L - 3av²uL)/(v-u)² = 0

Multiply both sides by (v-u)² to give;

(2av³L - 3av²uL) = 0

Thus, 2av³L = 3av²uL

Like terms cancel to give;

2v = 3u

Thus, v = 3u/2

To minimize a function, means that we want to get the minimum value of the function.

The value of v, that minimizes E is: [tex]\mathbf{v = \frac{3u}{2}}[/tex]

The function is given as:

[tex]\mathbf{E(v) = \frac{av^3L}{v - u}}[/tex]

First, we differentiate E(v) with respect to E using the quotient rule.

Quotient rule states that:

[tex]\mathbf{y' = \frac{V u' - Uv'}{v^2}}[/tex]

Using the above rule, we have:

[tex]\mathbf{E' = \frac{(v - u) \times 3av^2L - av^3L \times (-u)}{(v - u)^2}}[/tex]

To minimize the function, we set the equation to 0

[tex]\mathbf{\frac{(v - u) \times 3av^2L - av^3L \times (1)}{(v - u)^2} = 0}[/tex]

Cross multiply

[tex]\mathbf{(v - u) \times 3av^2L - av^3L = 0}[/tex]

Rewrite as:

[tex]\mathbf{(v - u) \times 3av^2L = av^3L }[/tex]

Divide through by av^2L

[tex]\mathbf{(v - u) \times 3 = v }[/tex]

Open brackets

[tex]\mathbf{3v - 3u = v}[/tex]

Collect like terms

[tex]\mathbf{3v - v = 3u}[/tex]

[tex]\mathbf{2v = 3u}[/tex]

Divide both sides by 2

[tex]\mathbf{v = \frac{3u}{2}}[/tex]

Hence, the value of v, that minimizes E is: [tex]\mathbf{v = \frac{3u}{2}}[/tex]

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