Answer:
There is only a beat frequency when the frequency heard (perhaps a tuning fork) is different from the frequency from the object in question (piano string, etc.).
The beat frequency equals the difference of the frequencies of the sources.
Wavelength = (speed)/(frequency) = 300,000,000/120,000,000 = 2.5 meters
Draw a free body diagram to help you visualize. draw the object and use arrows to label and determine where all the forces acting upon it will be. then u add up the sum of all forces. if two forces of equal magnitude and opposite directions will cancel each other out.
