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SLAY THE P.E. BLOG

Dissecting the Mechanical PE - Machine Design and Materials Exam: Problem 513

2/6/2017

2 Comments

 
Picture
Photo via : Les Chatfield
In the NCEES "Sample Questions + Solutions" book, the problems for the afternoon section are numbered 501 through 540. This post is about Problem 513 of the Machine Design and Materials exam.
Description of Problem 513: The problem statement shows a sketch of a cantilever beam. The beam is subject to a distributed load of constant magnitude in a section of its length. You are asked to obtain the internal shear force at a certain location within the beam.

Analysis of Problem 513: This kind of problem is most easily handled with the method of sections: You make a "cut" of the beam at the location of interest - thus "splitting" the beam into two sections. Then apply the equations of equilibrium to one of the two sections. Problem 513 is easier than most solved examples found on this topic in any Strength of  Materials textbook. Here's a similar problem inspired by a solved example we find in Mechanics of Materials by R.C. Hibbeler

Machine Design and Materials Exam Sample Problem #2
The beam is subject to a distributed load as shown:
Picture
The magnitude of the internal shear force (kip) at point A (10 ft from the fixed support) is nearest:


(A) 17
(B) 38
(C) 54
(D) 108

You may download the solution from the link below. Have any questions? Need help? Leave a comment below!
mech-dissecting-02-solution.pdf
File Size: 23 kb
File Type: pdf
Download File

2 Comments
Shing He
8/15/2017 08:59:50 pm

The first free body should be the entire system to find reaction force at the wall. The second free body should be the left hand side of point A.

This would be much faster to get the result.

Reply
Slay the PE
8/18/2017 12:17:17 pm

Hi!
Thanks for your comment. We appreciate all feedback!

In our solution we only use one FBD; the one for the section to the right of the cut. This eliminates the need to determine the wall reaction.

Analyzing two FBDs would be more time consuming, but in this particularly easy problem, it wouldn't really make much of a difference.

Reply



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