Wave Amplitude and Knot Movement

[Hughey85]

A 4.0 Hz wave with an amplitude of 12 cm and a wavelength of 30.0 cm travels along a stretched string.

(a) How far does the wave travel in a time interval of 3.0 s?
m

(b) How far does a knot on the string travel in the same time interval?
m


I got the answer to part (a) by using: x= lambda x (time/frequency)
The answer I got for it was 3.6 m.
I don't know what to do for part (b) Something to do with the amplitude, but I'm not sure...pls help! Thanks!

 

[Sirus]

Consider that a knot on the string reaches its amplitude peak four times each second. (also remember that a point on a string is not displaced horizontally when the string undergoes wave motion).

 

[Hughey85]

ok...so, how would I figure (b) out? Since the amplitude is reached 4 times in a second, and the time interval is 3 seconds, and the amplitude is 12 cm, how would you figure out the distance traveled?

 

[Leo32]

Just a small refrase of your last message:

you reach the amplitude of 12 cm 4 times per second for an interval of 3 seconds...

This might enable you to see the answer...

Regards,
Leo