Question

An object moving at a speed greater than that of sound is said to be moving at:
(A) infrasonic speed
(B) sonic speed
(C) ultrasonic speed
(D) supersonic speed

Answer 1

Hint:Sonic speed is another term for the speed of sound whereas infrasonic and ultrasonic our terms used to determine the frequency of the sound vibration.

Complete step by step answer:
An object is moving at a speed greater than that of sound. The term which is used to define that speed is known as supersonic speed. If an object is moving at a speed faster than sound, then it is set to be supersonic. When an object moves at supersonic speeds, then it experiences a phenomenon known as sonic boom. Sonic boom is a kind of large sonic explosion (i.e. a large sound with a huge vibration) which is observed when an object crosses the sound speed barrier achieving the supersonic speed.
Speed of sound in air is also defined in machs. One mach is the speed of sound in air and it is usually defined for supersonic objects which achieve speeds of greater than one mach. Jet planes achieve speeds of Mach 5 to 10. Sonic is the term used for anything which is related to sound. Sonic speed is nothing but the speed of sound.
Here sonic and supersonic are terms used to define the speed of sounds whereas infrasonic and ultrasonic have no relation to the speeds, instead they determine the frequency of sound vibration. Infrasonic sound is the sound whose frequency is below 2 Hertz i.e. the minimum frequency that can be heard. Ultrasonic sound is the sound whose frequency is above 20,000 Hertz i.e. the maximum frequency that can be heard. Both infrasonic and ultrasonic sounds cannot be heard by the human ear.
Hence, option (D) is the correct answer.

Note: Both infrasonic and ultrasonic does not signify anything related to the speed of sound. They are determined only by the frequency of the sound vibrations.