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STATICS - CASE STUDY

    Introduction


Problem Description
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Susan, a new engineering student, is being very careful to write down each calculation step as she proceeds through a complex problem. Her friend Sam, on the other hand, wants to round all numbers to only two digits to get done faster.

What is known:

  • The traffic light weighs 146.7 lb.
  • Cable A is 17.49° from the horizontal.
  • Cable B is 11.46° from the horizontal.
   
    Questions


What is Statics?
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What is the tension in both cables using four significant digits and two significant digits? Does rounding numbers to only two digits still provide an accurate answer?

    Approach


Force Diagram
 
  • Solve the problem using the basic steps in engineering problem solving: 1) read 2) draw diagrams 3) write equations 4) solve and 5) check.
  • For step 3, use the summation of forces in both the x and y directions:

                      ΣFx = 0        ΣFy = 0
  • Solve twice, once with four significant digits and once with two significant digits.