# 720 Two triangles | Centroid of Composite Area

Problem 720

The centroid of the sahded area in Fig. P-720 is required to lie on the y-axis. Determine the distance b that will fulfill this requirement.

Problem 720

The centroid of the sahded area in Fig. P-720 is required to lie on the y-axis. Determine the distance b that will fulfill this requirement.

**Direct Variation / Directly Proportional**

k = constant of proportionality

y varies directly as x is another statement equivalent to the above statement.

**Inverse Variation / Directly Proportional**

k = constant of proportionality

**Problem 14**

Find the angles that the diagonals of the rectangular parallelepiped 2 in. by 3 in. by 4 in. makes with the faces.

**Problem 13**

The figure represents a rectangular parallelepiped; AD = 20 in., AB = 10 in., AE = 15 in.

(a) Find the number of degrees in the angles AFB, BFO, AFO, BOF, AOF, OFC.

(b) Find the area of each of the triangles ABO, BOF, AOF.

(c) Find the perpendicular distance from B to the plane AOF.

**Solution 13**

**Problem 12**

In the figure is shown a rectangular parallelepiped whose dimensions are 2, 4, 6. Points A, B, C, E, F, and L are each at the midpoint of an edge. Find the area of each of the sections ABEF, ABC, and MNL.

**Solution 12**

**Problem 9**

A solid concrete porch consists of 3 steps and a landing. The steps have a tread of 11 in., a rise of 7 in., and a length of 7 ft.; the landing is 6 ft. by 7 ft. How much material was used in its construction?

**Problem 8**

An electric refrigerator is built in a form of rectangular parallelepiped. The inside dimensions are 3 ft. by 2.6 ft. by 1.8 ft. A freezing unit (1.1 ft. by 0.8 ft. by 0.7 ft.) subtracts from the storage room of the box. Find the capacity of the refrigerator.

**Problem 7**

The edges of the trunk are 3 ft., 4 ft., 6 ft. A second trunk is twice as long; the other edges are 3 ft., 4 ft. How do their volumes compare?

**Problem 6**

A tank, open at the top, is made of sheet iron 1 in. thick. The internal dimensions of the tank are 4 ft. 8 in. long; 3 ft. 6 in. wide; 4 ft. 4 in. deep. Find the weight of the tank when empty and find the weight when full of salt water. (Salt water weighs 64 lb/ft^{3} and iron is 7.2 times as heavy as salt water.

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