To develop this problem it is necessary to apply the concepts related to Wavelength, The relationship between speed, voltage and linear density as well as frequency. By definition the speed as a function of the tension and the linear density is given by

Where,
T = Tension
Linear density
Our data are given by
Tension , T = 70 N
Linear density , 
Amplitude , A = 7 cm = 0.07 m
Period , t = 0.35 s
Replacing our values,



Speed can also be expressed as

Re-arrange to find \lambda

Where,
f = Frequency,
Which is also described in function of the Period as,



Therefore replacing to find 


Therefore the wavelength of the waves created in the string is 3.49m
The distance is 30 km and the displacement is 22.4 km North East
I found this on arxsiv.org: “The central force motion between two bodies about their center of mass can be reduced to an equivalent one body problem in terms of their reduced mass m and their relative radial distance r. ... The potential V (r) from which this force is derived is also a function of r alone, F = −VV, V ≡ V (r).”
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