a microwaveable cup - of - soup package needs to be constructed in the shape of cylinder to hold 600 cubic…

a microwaveable cup - of - soup package needs to be constructed in the shape of cylinder to hold 600 cubic centimeters of soup. the sides and bottom of the container will be made of styrofoam costing 0.02 cents per square centimeter. the top will be made of glued paper, costing 0.05 cents per square centimeter. find the dimensions for the package that will minimize production cost. helpful information: h : height of cylinder, r : radius of cylinder volume of a cylinder: v = πr²h area of the sides: a = 2πrh area of the top/bottom: a = πr² to minimize the cost of the package: radius: cm height: cm minimum cost: cents
Answer
Explanation:
Step1: Express height in terms of radius
Given $V=\pi r^{2}h = 600$, so $h=\frac{600}{\pi r^{2}}$.
Step2: Write the cost - function
The cost of the bottom and sides is $0.02$ cents per square centimeter and the cost of the top is $0.05$ cents per square centimeter. The cost function $C(r)$ is $C(r)=0.02(2\pi r h+\pi r^{2})+0.05\pi r^{2}$. Substitute $h = \frac{600}{\pi r^{2}}$ into the cost - function: [ \begin{align*} C(r)&=0.02\left(2\pi r\times\frac{600}{\pi r^{2}}+\pi r^{2}\right)+0.05\pi r^{2}\ &=0.02\left(\frac{1200}{r}+\pi r^{2}\right)+0.05\pi r^{2}\ &=\frac{24}{r}+0.02\pi r^{2}+0.05\pi r^{2}\ &=\frac{24}{r}+0.07\pi r^{2} \end{align*} ]
Step3: Find the derivative of the cost - function
Differentiate $C(r)$ with respect to $r$: $C^\prime(r)=-\frac{24}{r^{2}} + 0.14\pi r$.
Step4: Set the derivative equal to zero and solve for $r$
[ \begin{align*} -\frac{24}{r^{2}}+0.14\pi r&=0\ 0.14\pi r&=\frac{24}{r^{2}}\ 0.14\pi r^{3}&=24\ r^{3}&=\frac{24}{0.14\pi}\ r^{3}&=\frac{120}{0.7\pi}\ r&\approx\sqrt[3]{\frac{120}{0.7\pi}}\approx\sqrt[3]{\frac{120}{2.1991}}\approx\sqrt[3]{54.56}\approx3.79 \end{align*} ]
Step5: Find the height
Substitute $r\approx3.79$ into $h=\frac{600}{\pi r^{2}}$: $h=\frac{600}{\pi\times(3.79)^{2}}\approx\frac{600}{45.16}\approx13.28$.
Step6: Find the minimum cost
Substitute $r\approx3.79$ into the cost - function $C(r)$: [ \begin{align*} C(3.79)&=\frac{24}{3.79}+0.07\pi\times(3.79)^{2}\ &\approx6.33 + 0.07\times3.14\times14.36\ &\approx6.33+3.14\ &\approx9.47 \end{align*} ]
Answer:
Radius: $3.79$ cm Height: $13.28$ cm Minimum cost: $9.47$ cents