wave question!!!

[peacefulheart]

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One end of a string is shaken each second sending a wave
with an amplitude of 10 em toward the other end. The
string is 5 meters long, and the wavelength of each wave
is 50 em. How many waves reach the other end of the
string in each 10 second interval?
A. 2
B. 5
C. 10
D. 50

 

[dechristine]

The answer is C) 10.

You're given that one end of the string is shaken each second, which means that one complete (wave) cycle happens every second, so the frequency f is 1/s.

velocity = wavelength * frequency. So, the waves are traveling at 50 cm/s. Since time = distance / velocity, it takes 500 cm / 50 cm/s = 10 s for one wave to travel from one end of the string to the other.

Remember, though, that the starting end of the string is shaken once each second. Even though it takes an individual wave ten seconds to reach the other end of the string, a (different) wave also hits the end of the string once each second. Thus, in 10 seconds, 10 waves reach the other side of the string.