What is the frequency of the siren's sound that the fire engine's driver hears reflected from the back of the truck?

i would like to make dinner for my mom, dad, and sister

molecules are free to separate from each other and will take on the shape of the container. molecules move completely at random and high speeds. they vibrate in a fixed position and do not move around much. molecules expand to the edge of their container.

snell's law

refractve index = sin incidence / sin refraction