Answer:
![a=(\pi)/(3)](https://img.qammunity.org/2021/formulas/physics/high-school/svhgijjxqr3orbea9l2pzilul4mgn7szje.png)
Step-by-step explanation:
given,
Amplitude ,A= 20 cm
distance between distance between two particle,y = 20 cm
Let equation of two SHM be x = A sin (ωt) and x = A sin (ωt + a)
where A is amplitude , ω is angular frequency and a is the phase difference.
now,
Distance between two particle at time t
y = A(sin(ωt+a)- sin (ωt))
using identity
![sin A - sin B = 2sin((A-B)/(2))cos((A+B)/(2))](https://img.qammunity.org/2021/formulas/physics/high-school/it0r1poptv8owhh9z54ilh97gsatjdnv68.png)
![y = A(2sin((a)/(2))cos((2\omega t + a )/(2)))](https://img.qammunity.org/2021/formulas/physics/high-school/ojbqkpo0zmu84iju6ssnxkzh7ckn36qxcs.png)
for maxima
![cos((2\omega t+a)/(2)) = 1](https://img.qammunity.org/2021/formulas/physics/high-school/9twljue1aak1jjiyxbfjcqavkp925m27zm.png)
maximum distance
![y = A(2sin((a)/(2)))](https://img.qammunity.org/2021/formulas/physics/high-school/8kcjkt49v9b718ximpojery299n411py89.png)
![20 = 20 * 2 sin((a)/(2))](https://img.qammunity.org/2021/formulas/physics/high-school/wxf7rynkn2qdw8g54n6gujq01iq8wkjj3e.png)
![sin((a)/(2))=(1)/(2)](https://img.qammunity.org/2021/formulas/physics/high-school/rchw29rm4z7gw9kkxi2pwng93ab92wj49r.png)
![sin((a)/(2))=sin((\pi)/(6))](https://img.qammunity.org/2021/formulas/physics/high-school/63ufcpu6ba3t5j2o3jkpmy6hrsk42x8yiy.png)
![(a)/(2)=(\pi)/(6)](https://img.qammunity.org/2021/formulas/physics/high-school/d8jb2m1r56nolt7i3pmkhnd1499lylsjji.png)
![a=(\pi)/(3)](https://img.qammunity.org/2021/formulas/physics/high-school/svhgijjxqr3orbea9l2pzilul4mgn7szje.png)
hence, the phase difference between the two particle is equal to
![a=(\pi)/(3)](https://img.qammunity.org/2021/formulas/physics/high-school/svhgijjxqr3orbea9l2pzilul4mgn7szje.png)