
The position of a particle performing an SHM is given by:
x=Asin(ωt+ϕ)
Since at t=0s, the particle is at x=0, therefore the initial phase ϕ=0.
At time t=2s, the particle is at x=2A.
∴2A=Asin(2ω)⇒ω=12πs−1
Therefore, time period
T=ω2π=24s
The total time taken from x=0 to x=A is 4T=6s.
Since the time taken from x=0 to x=2A is 2s, therefore the time taken from x=2A to x=A is 4s.