Question

I need the solution for 18th question

Answer 1

Option (4) 2 π/3

SHM are :    x1 = A Sin ωt
                    x2  = A Sin (ω t + Ф),  with a phase difference.

Let us say, at time t = t1, 
      x1 = A Sin ω t1 = A / 2
           => ω t1 = π/6          ---(1)

      x2 = A sin (ω t1 + Ф) = A / 2
            => ω t1 + Ф = 5π / 6    --- (2)

 Subtracting (1) from (2):        Ф = 2π/3