1. in which medium does sound travel the fastest?
a. salt water
b. fresh water
c. air
d. cast iron
2. a wave has a wavelength of 10 mm and a frequency of 5 hertz. what is its speed?
a. 50 mm/s
b. 50 hertz/s
c. 2 mm/s
d. 0.50 mm/s
3. how does reflection differ from refraction and diffraction?
a. reflection is the only process in which the wave does not continue moving forward.
b. reflection is the only process that involves a change in the wave.
c. reflection affects all types of mechanical waves, but refraction and diffraction do not.

1- CAST IRON

2- 50 mm/s

3-  Reflection is the only process in which the wave does not continue moving forward.

a longitudinal wave moves energy that is to the direction of the wave’s movement. - true

the box does not move because you need to use a force greater than 300 n. you are only using 50 n. it needs to at least be 301 n for the box to move because then it is an unbalanced force and it will move the way that the greater force is pushing it. if you use only 300 n it will be a balanced force and will not move because the force you are exerting on the   box is the same as its force.

hope this !

im sorry if i went too in depth, i am going to include a link to a video on khan academy that will explain this.   hope that you like the video and that it explains more in detail to you.

that is the link.