Daniel is standing a certain distance from a wall and claps. He hears the echo 4s later. How far away is the wall? Remember that the sound has travelled to the wall and come back.
(Take the speed of sound in air to be 330 m/s).

Your target variable is δf, the magnitude of the difference in frequency between the waves emitted from the sonar device and the waves received by the device after reflecting off the whale. write an expression for δf in terms of the relevant frequencies using the subscript notation introduced above.

Anybody wanna ? (picture included? )

In a good thermo flask the main cause of heat loss is