A uniform 3.0 m long aluminium rod is 3.0 m long is attached to a wall with a frictionless hinge. It is then held in a horizontal position at its other end by

A uniform 3.0 m long aluminium rod is 3.0 m long is attached to a wall with a frictionless hinge. It is then held in a horizontal position at its other end by a vertical very light string (see figure). What is the angular acceleration of the rod just after the string is released?
 

A.15 rad/s2

B.3.3 rad/s2

C.1.1 rad/s2

D.4.9 rad/s2

E.It cannot be calculated without knowing the mass of the rod.