Why do sound waves do not travel in empty space ?

a. because sound waves do not need matter to travel.

b. because sound waves need matter to travel.

c. because sound waves need vacuum to travel.

d. none of the above

Ball b is hanging from an inextensible cord. an identical ball a is released from rest when it is just touching the cord and drops through the vertical distance h a 5 8 in. before striking ball b. assuming e 5 0.9 and no friction, determine the resulting maximum vertical displacement h b of the ball b

Ammonia enters the expansion valve of a refrigeration system at a pressure of 10 bar and a temperature of 18oc and exits at 6.0 bar. the refrigerant undergoes a throttling process. determine the temperature, in oc, and the quality of the refrigerant at the exit of the expansion valve.

When the magnetic domains in a material can be aligned, but eventually drift out of alignment, the material is