Correktions and Hints
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6.4   I corrected the values of the viscosities for air and water.
      In e) and f) you will find an effect of friction that are *much* smaller
      than you might expect. Think about the friction discussed in 6.5 if
      that puzzles you.

6.6   I forgot to update the name of the problem, which is now
      "Maximum distance of flight."