A string with length of 0.5 m produces a musical sound travelling at a speed of 320 m/s find the fifth overtone I NEED HELP

Lets say that an object of a certain volume has a certin mass. what happens to its mass when you double its volume?

The place you get your hair cut has two nearly parallel mirrors 6.00 m apart. as you sit in the chair, your head is 2.00 m from the nearer mirror. looking toward this mirror, you first see your face and then, farther away, the back of your head. (the mirrors need to be slightly nonparallel for you to be able to see the back of your head, but you can treat them as parallel in this problem.) how far away does the back of your head appear to be?

The softest and hardest minerals are: softest hardest