
In circular motion with constant speed, magnitude of instantaneous velocity, vins=ωr.
Time taken to turn by 90∘ will be =ω2π=2ωπ.
Displacement will be equal to the length of AB=r2+r2=r2
Average velocity
vavg=timedisplacement=πr2×2ω=π22ωr
Hence, required ratio vavg vins =22ωrωrπ=22π
Therefore, x=2.