2011 Mechanical Systems - e3-ncees · PDF filePE principles and practice of engineering ......

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mechanical: MECHANICAL SYSTEMS and MATERIALS

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Copyright ©2011 by NCEES. All rights reserved. All NCEES sample questions and solutions are copyrighted under the laws of the United States. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means without the prior written permission of NCEES. Requests for permissions should be addressed in writing to [email protected]. NCEES PO Box 1686 Clemson, SC 29633 800-250-3196 www.ncees.org ISBN 978-1-932613-60-5 Printed in the United States of America November 2010 First printing April 2013 Second printing


iii

CONTENTS Introduction to NCEES Exams ................................................................ 1

About NCEES

Updates on exam content and procedures

Exam-day schedule

Admission to the exam site

Candidate Agreement

Scoring and reporting Exam Specifications .......................................................................... 3

Sample Questions and Solutions

Morning Sample Questions ................................................................. 9

Afternoon Sample Questions ............................................................. 27

Morning Solutions .............................................................................. 49

Afternoon Solutions ........................................................................... 65

Psychrometric Chart ....................................................................... 81


1

About NCEES NCEES is a national nonprofit organization dedicated to advancing professional licensure for engineers and surveyors. It develops, administers, and scores the examinations used for engineering and surveying licensure in the United States. It also facilitates professional mobility and promotes uniformity of the U.S. licensure processes through services for its member licensing boards and licensees. These services include the records program, study materials, credentials evaluations, exam administration, and more. NCEES is composed of member licensing boards from throughout the United States and its territories. Updates on exam content and procedures NCEES.org is our home on the Web. Visit us there for updates on everything exam-related, including specifications, exam-day policies, scoring, and corrections to published study materials. This is also where you will register for the exam and find the additional steps you should follow in your state to be approved for the exam. Exam-day schedule Be sure to arrive at the exam site on time. Late-arriving examinees will not be allowed into the exam room once the proctor has begun to read the exam script. The report time for the exam will be printed on your Exam Authorization. Normally, you will be given 1 hour between morning and afternoon sessions. Admission to the exam site To be admitted to the exam, you must bring two items: (1) your Exam Authorization and (2) a current, signed, government-issued photo identification. Candidate Agreement The NCEES Candidate Agreement describes references and other personal materials allowed in the exam room. It also describes other exam policies designed to protect exam content. This document will be printed in your exam book. It is also available for download at NCEES.org. If you register to take an NCEES exam, you are strongly encouraged to review this document prior to exam day, as you will be asked to affirm that you abide by the policies and procedures it describes. Scoring and reporting NCEES typically releases exam results to its member licensing boards 8–10 weeks after the exam. Depending on your state, you will be notified of your exam result online through your My NCEES account or via postal mail from your state licensing board. Detailed information on the scoring process can be found at NCEES.org.


9

MECHANICAL

MORNING SAMPLE QUESTIONS

A psychrometric chart (normal temperature at sea level) is provided on page 81 for your possible use. Unless

stated otherwise, assume sea level conditions.


MECHANICAL MORNING SAMPLE QUESTIONS

Copyright 2011 by NCEES 10 GO ON TO THE NEXT PAGE

101. Poisson's ratio is a term that arises in:

(A) heat transfer

(B) HVAC

(C) mechanical behavior

(D) vapor power cycles 102. Which of the following is used as a measure of energy efficiency of refrigeration systems?

(A) COP

(B) Hydraulic head

(C) Latent heat

(D) SHR 103. A system with an initial cost of $90,000 has an operating cost of $2.50/hr and is operated

16 hr/day for 300 days/year. After 10 years, the system has a salvage value of $10,000. Assuming the interest rate is constant at 10%, the total annualized cost over the 10-year life is most nearly:

(A) $12,000 (B) $14,000 (C) $20,000 (D) $26,000

104. You manage a manufacturing production department that operates 80 hr/week. The process has a

production rate of 60 units/hr, with a scrap rate of 1 out of 120 units. With a 10% lost production time allowance, the number of good units that can be made per week is most nearly:

(A) 4,284 (B) 4,320 (C) 4,760 (D) 4,800


MECHANICAL MORNING SAMPLE QUESTIONS


2,500 lbf

2

1

3

4

119. Which of the following factors is least likely to affect the fatigue life of a steel spring?

(A) Alternating stresses

(B) Cycle period

(C) Primary stresses

(D) Surface roughness 120. The 2,500-lbf load shown in the figure is supported by a beam that is secured by six 3/4-in.-

diameter bolts in a hexagonal array with neighboring bolts 3 in. apart. The shear stress is greatest in which bolt?

(A) 1 (B) 2 (C) 3 (D) 4


27

MECHANICAL SYSTEMS AND MATERIALS

AFTERNOON SAMPLE QUESTIONS

A psychrometric chart (normal temperature at sea level) is provided on page 81 for your possible use. Unless

stated otherwise, assume sea level conditions.


MECHANICAL SYSTEMS AND MATERIALS AFTERNOON SAMPLE QUESTIONS


O.D.

twall

NOT TO SCALE

b

c

F = 9 kN

a

a

2

12 in. 12 in.

501. A bracket is constructed using two tubes and a solid plate as shown in the figure below. Assume each tube is rigidly attached to the plate and fixed against bending and twisting on the other end. The dimensions are as follows:

a = 900 mm b = 600 mm c = 250 mm

Which dimensions are necessary and sufficient to determine the reaction at the end of each tube? (A) a, b only (B) a, b, c (C) b only (D) b, c only

502. A 24-in.-long cantilever beam carries a uniformly distributed load of 10 lb/in. over 12 in. as

shown in the figure. The shear force (lb) in the beam at a distance of 18 in. from the wall is most nearly:

(A) 60 (B) 75 (C) 90 (D) 120




P

C

D

B

A

10 in.

20 in.

30°45°

523. The figure below shows a schematic of a can-crushing device. The device consists of a slider at A. The slider moves in a horizontal guide with an opening to discharge the crushed can. Pin joints connect Links ABC, BD, and the slider at A. All links and pins at ABD are made with materials having the following physical properties:

Modulus of elasticity 30 106 psi Yield strength, Sy 60,000 psi Ultimate strength, Su 100,000 psi Shear strength 20,000 psi

Link BD, of length 7.07 in., is made out of a solid bar of circular cross section and is designed to carry an axial load of 500 lb. A safety factor of 2 against yield and 1.5 against buckling is desired for safety reasons. The diameter (in.) of the bar used for Link BD is most nearly: (A) 0.103 (B) 0.146 (C) 0.184 (D) 0.225




20 in.

3 in.

BEARING 4

1-in. LEAD SCREW

5 in.

W

BEARING 1

BEARING 3

Z

Y X

G2

G1

1-in.-DIAMETER SHAFT

MOTOR/ENCODER

BEARING 2

48 in.

1-in.

DIAMETER

2 in. (TYP.)

LEAD SCREW

BEARING

Y

536. An initial analysis must be performed on the design of a proposed linear positioning system as shown in the figure. All components are steel unless otherwise noted. Other Data:

Size of table 20 16 1 in. No. of teeth on G1 16 No. of teeth on G2 48 Pitch of lead screw 0.125 in. Length of lead screw 48 in. Root diameter of lead screw 0.84 in. E for steel 30,000,000 psi

The critical speed (rpm) of the lead screw prior to the installation of the table can be approximated from:

critical speed2

215 gEI

ρAL

where:

L = lead screw length (in.) E = modulus of elasticity (psi) I = moment of inertia (in4) = density (lb/in3) A = cross-sectional area (in2)

The critical speed (rpm) is most nearly: (A) 1,150 (B) 3,950 (C) 91,250 (D) 190,000

49

MECHANICAL

MORNING SOLUTIONS


MECHANICAL MORNING SOLUTIONS

51

CONSECUTIVE DAYS TASK AND DURATION PLANNED

REVISED-ACTUAL

A (2) B (2) C (7)

D (11) E (2)

E (2)

0 2 4

13 14 15

16

101. Poisson's ratio is a measure of how a material deforms when acted upon by a force. It is applied in situations where the mechanical behavior of a machinery component is important.

THE CORRECT ANSWER IS: (C)

102. The coefficient of performance (COP) is a measure of energy efficiency of refrigeration systems.

THE CORRECT ANSWER IS: (A)

103. Annualized purchase price over 10 years $90,000 (A/P, 10%, 10) = 0.1627

Annualized salvage value after 10 years $10,000 (A/F, 10%, 10) = 0.0627

Annual operating cost = (300 days/yr)(16 hr/day)($2.50/hr) = $12,000

Total annual cost = $90,000(0.1627) – $10,000(0.0627) + $12,000 = $26,016

THE CORRECT ANSWER IS: (D) 104. 80 hours – 10% lost production time = 72 hours

72 hours × 60 units/hour = 4,320 units 1 scrap/120 units × 4,320 units = 36 scrap 4,320 – 36 units = 4,284 units


105. If Task C is delayed by 3 days, but has 2 days to spare while waiting on Task D, then the total

compensation delay will be 1 day of delivery time.

THE CORRECT ANSWER IS: (B)


65

MECHANICAL SYSTEMS AND MATERIALS

AFTERNOON SOLUTIONS


MECHANICAL SYSTEMS AND MATERIALS AFTERNOON SOLUTIONS

67

SHEAR FORCE DIAGRAM

120 in.

12 in. 12 in.18 in.

x

200 N 400 N

350

2 m2 m 4 m

150

1000

A B

700

ΣMB = 0

−8A + 1,200 + 1,600 = 0

8A = 2,800

A = 350 N ⇒ B = 600−350 = 250 N

Maximum moment = 1,000 N•m

SHEAR FORCE DIAGRAM

BENDING MOMENT DIAGRAM

MOMENT(N•m)

SHEAR(N)

−250

501. Dimension a is needed to determine the moment reactions. Dimension b is needed to determine torque reactions. Dimension c is not needed.


502.

x 120

6 12 lb60x


503.



PE Sample Questions and Solutions Published by NCEES

Chemical

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Civil: Structural

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Mechanical: Thermal and Fluids Systems

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2011 Mechanical Systems - e3-ncees · PDF filePE principles and practice of engineering ......

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