A professor's office door is 0.92 {rm m} wide, 2.2 {rm m} high, 4.0 {rm cm} thick; has a mass of 30 {rm kg}, and pivots on frictionless hinges. A "door closer" is attached to door and the top of the door frame. When the door is open and at rest, the door closer exerts a torque of 5.4 {rm N}cdot {rm m}.
A: What is the moment of inertia of the door?
B: If you let go of the open door, what is its angular acceleration immediately afterward?