The whole definition of frequency is: <em>How often something happens. </em>
Especially referring to something that happens over and over and over and over.
One example is Choice-C: How often the particles of a medium vibrate.
"Frequency" comes from the word "frequent". That means "often", and "frequency" just means "often-ness" ... HOW often the thing happens.
Some other examples:
Frequency of jump-roping . . . maybe 60 per minute .
Frequency of rain . . . maybe 5 per month .
Frequency of an AM radio station . . . maybe 1 million waves per second.
(If it's something <u><em>per second</em></u>, then we call it "Hertz". That's not for the car rental company. It's for Heinrich Hertz, the German Physicist who was the first one to prove that electromagnetic waves exist. He sent radio waves all the way ACROSS HIS LABORATORY and detected them at the other side ( ! ), in 1887.)
Frequency of the wiggles in the sound wave coming out of a trumpet playing the note ' A ' . . . 440 Hertz.
Frequency of sunrise and the Chicago Tribune newspaper . . . 1 per day
Frequency of the cycle of Moon phases and an average human woman's ovulation cycle: 1 per 29.531 days, 1 per ~28 days .
The answer would be C. (:
In order to draw the free body diagram, first let's calculate the friction force acting on the crate:

Since the friction force is greater than the force applied, the crate will not move, and the friction force will be equal to the force applied.
The weight force is equal to 40 * 9.8 = 392 N.
So, drawing the diagram, we have:
Answer:
The idea behind space expansion is that after the big bang, the universe started infinitely expanding. It's also called metric expansion. Stephen Hawking's A Brief History of Time goes further into detail on this.
Answer:
895522 times faster.
Explanation:
From the question given above, the following data were obtained:
Speed of sound in air (v) = 335 m/s
Speed of light in air (c) = 3×10⁸ m/s
How many times faster =.?
To obtain how many times faster light travels in air than sound, do the following
c : v => 3×10⁸ : 335
c/v = 3×10⁸ / 335
c/v = 895522
Cross multiply
c = 895522 × v
From the illustrations made above, we can see that the speed of the light in air (c) is 895522 times the speed of sound in air.
Thus, light travels 895522 times faster than sound in air.