A worker was working on the rail track. A boy at a distance holds his ear near the rail track. This boy was able to hear sound of the blow of workman twice. It is because of :

When the same tone is played on a sitar and a fute, the sound produced can be distinguished from each other because of the diference in :

SONAR is a device that is used to measure the distance of underwater objects by a ship. Which of the following types of waves does it use for this purpose?

How much should minimum distance be between the source of sound and reflecting surface, so that an echo can be heard clearly?

A sound wave having frequency of 300 Hz is travelling in an unknown medium. Its wavelength is not known. It travels a distance equal to 150 times its wavelength in time t. The value of t is :

An astronaut cannot hear his companion at the surface of the moon because –