The siren of a fire engine that is driving northward at
30.0 m/s emits a sound of frequency 2000 Hz. A truck in front of
this fire engine is moving northward at 20.0 m/s. (a) What is the
frequency of the siren’s sound that the fire engine’s driver hears
reflected from the back of the truck? (b) What wavelength would
this driver measure for these reflected sound waves?