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Problem on Order of magnitude estimates for events in daily life

  1. May 17, 2013 #1
    Hi need help for order of magnitude estimates
    the question is give the numerical values for order of magnitude estimates for following . explain and justify assumptions
    (a) the number of cars that pass through an intersection of to busy streets during the evenning commune on a typical workday
    (b)the number of bricks that form the exterior of a large building on university campus
    (c) volume of concrete in the sidewalks of university campus
    (d) number of baseballs that an fit in a classroom
    (e) number of people who are born everyday


    Attempt at solution: i know assumptions have to be made for the different quantities. But dont know what is the magnitude of assumptions that need to be taken.
    Please help me out in this
     
  2. jcsd
  3. May 17, 2013 #2

    berkeman

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    Staff: Mentor

    Talk through question (b) -- it is the easiest one. What is the size of a typical building on your campus? What is the surface area of a brick and its associated mortar joint? Please show some effort so we can help you more...
     
  4. May 17, 2013 #3
    The question is just that.. we need to assume everything.. the question is what i have typed.. we need to assume all the quantities and then come up with an order of magnitude estimate.. its from the book introduction to mechanical engineering by jonathon wickert.. comes under the chapter problem solving..
     
  5. May 17, 2013 #4

    berkeman

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    So show some effort! This is your schoolwork question, and it is pretty easy at that. Show some attempts at working the problems or this thread will be deleted.
     
  6. May 17, 2013 #5
    ok so if i walk through the question (b) i first assume the size of the exterior of the building as a square of size 100 x 100 ft . the height as 100 ft. Now each brick is of size 1ft x 6 inches. i can actually get the number of bricks required from this.. but then how do i get an estimate range as i am coming with a definite answer
     
  7. May 17, 2013 #6

    berkeman

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    Staff: Mentor

    Good. That does give you an estimate, since you are using estimates of the surface area of the sides of the building and of the brick. You have not gone out and actually measured anything.

    Now have a go at the others and show your work. I bet you can get most of them now... :smile:
     
  8. May 17, 2013 #7
    Nobody expects you to get the exact answers to these questions. They just want to get you thinking out of the box on how you might go about getting an estimate. This is the type of thinking you may have to do sometimes during your career as an engineer. If you can give the answer to a factor of 10, that would be acceptable. If you can figure out a clever way of estimating to a factor of three, that would be even better. Just try to think of trying to make each of these estimates in more than one way. Here are some more questions of this type to consider:

    How many hospitals are there in your state? How much does your house weigh? How many fans are ejected from a ballpark each baseball season? How many foul balls? Cost of an average pizza? Number of employees in the federal government? What are the gross revenues of your favorite restaurant?

    Off hand, I don't know the answers to any of these questions, but I do know that if I wanted to estimate any of them, I could do better than just throwing my hands up in the air and giving up. I would come up with something. I'm confident that you can do the same.

    chet
     
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