## 56 - 57 Maxima and minima problems of square box and silo

Problem 56
The base of a covered box is a square. The bottom and back are made of pine, the remainder of oak. If oak is m times as expensive as pine, find the most economical proportion.
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Problem 57
A silo consists of a cylinder surmounted by a hemisphere. If the floor, walls, and roof are equally expensive per unit area, find the most economical proportion.

## 29 - 31 Solved problems in maxima and minima

Problem 29
The sum of the length and girth of a container of square cross section is a inches. Find the maximum volume.

Problem 30
Find the proportion of the circular cylinder of largest volume that can be inscribed in a given sphere.

Problem 31
In Problem 30 above, find the shape of the circular cylinder if its convex surface area is to be a maximum.

## 25 - 27 Solved problems in maxima and minima

Problem 25
Find the most economical proportions of a quart can.

Problem 26
Find the most economical proportions for a cylindrical cup.

Problem 27
Find the most economical proportions for a box with an open top and a square base.

## 21 - 24 Solved problems in maxima and minima

Problem 21
Find the rectangle of maximum perimeter inscribed in a given circle.

Problem 22
If the hypotenuse of the right triangle is given, show that the area is maximum when the triangle is isosceles.

Problem 23
Find the most economical proportions for a covered box of fixed volume whose base is a rectangle with one side three times as long as the other.

## 15 - 17 Box open at the top in maxima and minima

Problem 15
A box is to be made of a piece of cardboard 9 inches square by cutting equal squares out of the corners and turning up the sides. Find the volume of the largest box that can be made in this way.

Problem 16
Find the volume of the largest box that can be made by cutting equal squares out of the corners of a piece of cardboard of dimensions 15 inches by 24 inches, and then turning up the sides.

Problem 17
Find the depth of the largest box that can be made by cutting equal squares of side x out of the corners of a piece of cardboard of dimensions 6a, 6b, (b ≤ a), and then turning up the sides. To select that value of x which yields a maximum volume, show that

$( \, a + b + \sqrt{a^2 - ab + b^2} \, ) \, \ge \, 3b$

## Problem 310 - 311 | Equilibrium of Concurrent Force System

Problem 310
A 300-lb box is held at rest on a smooth plane by a force P inclined at an angle θ with the plane as shown in Fig. P-310. If θ = 45°, determine the value of P and the normal pressure N exerted by the plane.

## 245 - Couple in the box

Problem 245
Refer to Fig. 2-24a. A couple consists of two vertical forces of 60 lb each. One force acts up through A and the other acts down through D. Transform the couple into an equivalent couple having horizontal forces acting through E and F.

## 007 Components of a force parallel and perpendicular to the incline

Problem 007
A block is resting on an incline of slope 5:12 as shown in Fig. P-007. It is subjected to a force F = 500 N on a slope of 3:4. Determine the components of F parallel and perpendicular to the incline.