A cord is wound around the circumference of a bicycle wheel (without tyre) of diameter 1 m. A mass of 2 kg is tied to the end of the cord and it is allowed to fall from rest. The weight falls 2m in 4 s. The axle of the wheel is horizontal and the wheel rotates with its plane vertical. (Take g=10ms−2 ) then the angular acceleration of the wheel is (rad/s2)