Question

A box with a square base and open top must have a volume of 13,500 cm^3. Find the dimensions of the box (in cm) that minimize the amount of material used.

There are 2 answer, the height and the sides of the base.

Answer 1

Let the side length of the square base be x cm and the height of the box be h cm. Then the volume of the box is given by:

V = x^2 * h = 13,500 cm^3

We want to minimize the amount of material used, which is the surface area of the box. The surface area A is given by:

A = x^2 + 4xh

We can use the volume equation to solve for h in terms of x:

h = 13,500 / x^2

Substituting this into the surface area equation gives:

A = x^2 + 4x(13,500 / x^2) = x^2 + 54,000 / x

To minimize A, we take the derivative with respect to x and set it equal to zero:

dA/dx = 2x - 54,000 / x^2 = 0

Solving for x, we get:

x^3 = 27,000

x = 30

Substituting this back into the volume equation gives:

h = 13,500 / (30^2) = 15

Therefore, the dimensions of the box that minimize the amount of material used are 30 cm by 30 cm by 15 cm.