:shy: Any help will be apreciated. These are some pre-exam exercises that were given to my daughter I would like to be able to check the answers and help her with any difficulties. 1) A string, whose density is 0.01 kg/m, and whose length is of 60 cm is stretched with a tension of 576 newtons. a) What is the frequency of the third harmonic? b) At what point was the string plucked? 2) A tuning fork sounds the note A (440 Hz). What would you expect to happen if it was struck near the mouth of the closed tube (closed at one end). Explain why this happens. Would the sound of a tuning fork tuned an octave higher have the same effect? 3)If you hold down (without playin) the G on the piano, and then strike the lower D sharply, you will hear a note corresponding to the upper D. This can't come from the string that was hammered, as it stops vibrating as soon as you release the key, so where does it come from? Explain this, from what you know about string vibrations. Both this phenomenon, and the one discussed in question 2 are examples of a particular acoustic mechanism. What is it? Thanks alot!!!