To solve this problem we will apply the concept of Impulse. Which is described as the product between the Force and the change in time. Mathematically this can be described as

Where,
F = Force
= Time
Our values are given as,
F = 1450N

Replacing we have,


Therefore the impulse delivered to the soccer ball is
or 
When air is blown into the open pipe,
L = 
where nis any integral number 1,2,3,4 etc. and λ is the wavelength of the oscillation
⇒λ=
Note here that n=1 is for fundamental, n=2 is first harmonic and so on..
⇒ third harmonic will be n=4
Given L=6m, n=4, solving for λ we get:
λ=
=3m
Relationship of frequency(f), velocity of sound (c) and wavelength(λ) is:
c=f.λ Or f= 
⇒f=
≈115 Hz
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