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Textbook Answers Problems

  1. Jun 12, 2014 #1
    There is definitely something wrong with my textbook.
    Could you tell if ANY of the answers are actually correct? I'm trying to compare with my answers, but it's just plain impossible to decipher if I'm going crazy or not...

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  2. jcsd
  3. Jun 12, 2014 #2
    Here is 20.4's "answer."

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  4. Jun 12, 2014 #3
    Here is my attempt for 20.7. Could you please check this one? If I get it right, it probably means I get them all.

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  5. Jun 14, 2014 #4
  6. Jun 14, 2014 #5


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    Did find your 2.7 picture, but could not find your reasoning as to why it should look like this. But I do get the same snapshot.
    The book 2.4 snapshot picture seems to in error: by mistake they printed a copy of the history graph. (because the solution tekst matches the history picture)/
  7. Jun 14, 2014 #6


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    I can't make sense of any of the textbook answers.
    E.g. look at 20.6. The explanation given says
    The given history graph shows no such thing. (Neither does the other history graph, 20.7.) The negative portion doesn't arrive until t = 4.
    More generally, since all the graphs show displacements, and the waves are moving at constant speeds, the only differences between a history graph and a corresponding snapshot graph should be a possible left/right reversal and a possible left/right shift. Yet the answers for 20.5 and 20.6 do not match any of given graphs in that way.
    The only one that looks sort of right is 20.7, but the answer is still wrong. At x=2, t=0 in the given (snapshot) graph, the displacement has been zero but is about to go positive. In the answer given at x=2, the displacement is 1 for t in the range -1 to +1.
  8. Jun 14, 2014 #7


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    I didn't check all of them, but it looks to me like some sort of printing error, for example the file names for the images (which as haruspex said would look very similar) have got mixed up.

    If you ever try to proof-read a complete book, it's a lot to do harder than you might think. It's easy to "see what you expect to see", not what is actually on the page.
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