A C-130 Hercules is traveling toward a cliff

A C-130 Hercules is traveling toward a cliff at the speed of 150 m/s. Its engines emit a tone at frequency f0. We consider that the speed of sound is 340 m/s. What frequency is received by a pilot after reflection from the cliff?

Image Source: U.S. Air Force

A person hears the whistle of an approaching train

A person standing near a railway track hears the whistle of an approaching train as having a frequency of 1600 Hz. The train’s velocity is 40 m/s.
What is the true frequency of the sound emitted by the whistle?

A spacing of the interference fringes on a screen in Young’s experiment

How many times will increase a spacing of the interference fringes on a screen in Young’s experiment (Double-slit experiment), if a green (λ1 = 500 nm) filter is replaced by a red filter (λ2 = 750 nm)?

Image Credit: MIT

Is it possible to have lightning without thunder?

Often we see a flash of lightning, but do not hear the thunder. As a rule, thunder has a short range of detection — usually less than 25 km (15 miles). Why?

The longest wavelength.

Which of these waves have the longest wavelength?
a. infrared light
b. ultraviolet light