11. If a 1 kg spear is thrown at 10 m/s and gets imbedded into a 9 kg wooden box that was at rest, how fast does the wooden box and embedded spear move after the collision?

Astring vibrates with a frequency of 10 hz. why can't a person hear the sound waves produced by the vibrating string, no matter how large the amplitude of the waves? out! this is homework and due tomorrow! you so much!