# FE Civil Engineering Exam Prep #4

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#### What property of a metal refers to its ability to be hammered into sheets?

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Answer: Malleability Malleability refers to a metal’s ability to be hammered into sheets.

#### When considering the surface overflow rates of primary settling tanks in a typical municipal wastewater treatment plant, which of the following statements is not correct?

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The statement, “Sizing is based on the measured flow conditions” is not correct when considering the surface overflow rates of primary settling tanks. Typically, the primary settling tanks are sized based on the surface area calculations performed using 1) design average flow conditions and 2) design peak hourly flow conditions. The larger surface area of the two is used to size the primary setting tank. Specific design requirements for primary settling tanks are set by state regulating agencies.

#### 80.0 grams of NaOH is dissolved in 3.0 moles of H20. What is the mole fraction of NaOH in this solution?

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Answer: .40 The mole fraction for a compound indicates (moles of given compund) / (total moles of system). In this question, there are two moles of NaOH and five total moles in the system. Thus, the mole fraction is expressed as 2/5, or .40.

#### Cathodic protection is used to control which of the following?

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Cathodic protection is used to control corrosion. Corrosion is an electrochemical process in which an electrical current flows through a metallic substance, causing a chemical reaction that results in pitting and, ultimately, complete deterioration. Cathodic protection systems use the electrical properties of metallic substances to protect against the corrosion of metallic piping and structures by forcing an electrical interaction. There are two main types of cathodic protection systems: - Galvanic - uses a sacrificial anode, placed adjacent to the structure to be protected, that corrodes instead of the structure - Impressed current - a current is applied to a structure from an adjacent anode

#### What is the total volume of a grit chamber designed to handle an average daily flow of 3 million gallons with a peak flow ratio of 2.5, and a detention time of 3 minutes?

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The total volume of the grit chamber is 2,079 ft3 when required to handle an average flow of 3 million gallons per day (mgd), with a peak flow ratio of 2.5 and a detention time of 3 minutes. Solution: volume of grit chamber = peak flow x detention time Where peak flow = average flow x peak flow ratio = 3 mgd x 2.5 = 7.5 mgd Given 1 mgd = 1.54 ft3/sec Where detention time = 3 min x 60 sec/min = 180 sec Volume = 7.5 mgd x 1.54 ft3/sec x 180 sec = 2,079 ft3

#### The American Association of State Highway Transportation Officials (AASHTO) recommended stopping sight distances are based on the operation of which type of vehicle?

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AASHTO’s recommended stopping sight distances are based on the operation of a passenger car. In general, large trucks require a longer stopping distance than a passenger car. However, since drivers in large trucks sit higher up than a driver in a car, they are able to see substantially further down a roadway. AASHTO does not provide recommendations for bicycle or railroad car SSDs.

#### Which of the following compounds contains a double bond?

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Answer: C2H4 Hydrocarbons with the formula CnH2n contain double bonds. The only compound with this formula, C2H4, must contain a double bond.

#### When consuming drinking treated water, which of the following may be an indicator of water quality problems within a finished water storage facility?

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When drinking treating water, the presence of a poor taste or unpleasant odor, or the awareness of an ambient water temperature may indicate that there is a water quality problem within a finished water storage facility. Stale water within a storage facility promotes the growth of microorganisms that cause poor tastes or unpleasant odors and is often a result of water stored too long. Stagnant water will approach ambient temperatures, and may be a result of short-circuiting or accumulated sediment that impedes mixing within a storage unit.

#### What is the oxidation state of chlorine in potassium perchlorate, KClO4?

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Answer: 7 Begin this problem by considering the oxidation state of oxygen. As in most oxides, oxygen has an oxidation state of -2. Multiply this value by four to account for all of the oxygens, giving a total oxidation value of -8. Potassium has an oxidation state of +1, bringing the total oxidation value to -7. In order to maintain electrical neutrality, chlorine must have an oxidation state of +7.

#### A saturated solution of NaCl is heated until more solute can be dissolved. How is this solution best described?

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Answer: Supersaturated When a saturated solution is heated so more solute can be dissolved, the solution is described as supersaturated. Supersaturated solutions are typically unstable, and the solute can crash out of solution if a seed crystal is provided.

#### The half-life of 14 grams of a substance is 3 hours. How many grams of the substance remain after 6 hours?

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Answer: 3.5 grams The half-life of a substance is the amount of time required for that substance to decay to half of its original mass. In the context of this question, 6 hours represents two half-lives. Therefore, the substance will decay to one-fourth of its original mass, or 3.5 grams.

#### Which of the following hammers is not commonly used for conducting Standard Penetration Tests (SPTs)?

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A split-spoon is not a hammer used for conducting SPTs. A split spoon is a sampling tube, approximately 20 - 36-inches long, that is placed inside a drill rod to collect soil samples. Automatic, donut, and safety hammers are used to drive the drill rods into the soil.

#### The Association of American State Highway and Transportation Officials (AASHTO) assumes that the height of a driver’s eye and the height of an object above pavement are which of the following (in inches) when developing recommendations for minimum stopping sight distances?

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AASHTO assumes that the height of a driver’s eye and the height of an object above pavement are 42 inches and 24 inches (respectively) when developing recommendations for minimum stopping sight distances. AASHTO’s recommended distances are a conservative estimate of how long it will take a driver to perceive a situation exists that will require them to stop, apply the brakes, and come to a complete stop. The stopping site distance is an important safety consideration to assure that drivers have a continuous length of visible roadway.

#### The half-life of 32 grams of a radioactive substance is 6.5 hours. How many grams of the substance remain after 19.5 hours?

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Answer: 4 grams The half-life of a substance is the amount of time required for the substance to decay to half of its original mass. In the context of the question, 19.5 hours represents three half-lives. Therefore, the substance will be reduced to (1/2)3 or 1/8 its original mass. 1/8 x 32 gives the correct answer of 4 grams.

#### What is the passing sight distance for a section of 60 mph 2-lane rural highway with a 1740-ft vertical sag curve where a bridge passes over at 16.8 ft? (Assume S > L and A = 3.15.)

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The passing sight distance for a section of 60 mph 2-lane rural highway with a 1,740-ft vertical sag curve where a bridge passes over at 16.8 ft is 2,273 ft. Solution: Use sag vertical curve length at undercrossing equation (US Customary units) S = sigh distance = L/2 + [400(C-5.75)]/A Where: L = vertical sag length = 1740 ft C = bridge height = 16.8 ft A = % difference in grades = 3.15 And 5.75 = 0.5(object height + eye height) S = 1740/2 + [400(16.8-5.75)]/3.15 = 2,273 ft

#### Which of the following straight-chain hydrocarbons is classified as saturated?

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Answer: C2H6 Saturated straight-chain hydrocarbons contain only single bonds. As long as the saturated hydrocarbon does not contain a ring, it will obey the formula CnH2n+2. Thus, the saturated straight-chain hydrocarbon is C2H6.

#### Which of the following acids is classified as weak?

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Answer: CH3COOH A weak acid is an acid that does not dissociate completely in solution. HCL, HBr, HClO4, and H2SO4 are strong acids. CH3COOH is the weak acid.

#### Which of the following is a potential safety or operational issue associated with a bridge spanning a recently repaved roadway that now has a vertical clearance of 4-inches less than posted?

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All of the listed issues are potential safety and/or operational issues associated with a bridge spanning a recently repaved roadway that now a vertical clearance of 4-inches less than posted. Drivers of large vehicles depend on the posted clearance values to avoid collisions with the bridge structure. Collisions with overhead structures often lead to multiple crashes due to limitations on stopping site distances, design speeds, and traffic conditions. Traffic delays may result from overhead structure collisions, multiple vehicle crashes and repairs to the damaged structure.

#### Which of the following compounds is classified as a metallic oxide?

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Answer: Na2O Metallic oxides consist of an oxygen atom bound to a metal. The only metal present in this question is sodium, so Na2O must be a metallic oxide.

#### What is the proper sequence of steps to construct a dewatering wellpoint system for a construction excavation? 1. Connect header pipe to suction pumps 2. Jet wellpoints into the ground 3. Connect wellpoints to header pipe with riser 4. Fill annular void with filter media

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The proper sequence of steps to construct a dewater wellpoint system are as follows: 1. Jet wellpoints into the ground 2. Fill annular void with filter media 3. Connect wellpoints to header pipe with riser 4. Connect header pipe to suction pumps A wellpoint system used to dewater a construction excavation consists of a series of small-diameter wells that are closely spaced and installed at shallow depths. The wells are connected to a piping system that is attached to a vacuum pump and surrounds the excavation.