What is the awnser to blank occurs when a substance changes from a liquid to a gas

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.

In a voltaic cell, electrons flow from the (positive/negative) to the (positive/negative) terminal.

Which diagram correctly demonstrates the various forces acting on a ball moving horizontally with some speed?