Solution: A large door 2.0 m wide is initially at rest. The door is free to turn about frictionless hinges along one edge. A person applies a constant force F = 120 N perpendicular to the door at the edge opposite from the hinges, so a distance of 2.0 m from the line along the hinges. The force remains perpendicular to the door as the door rotates. The door turns through 90° in 4.0 s. What is the moment of inertia of the door for an axis along the hinges?

A large door 2.0 m wide is initially at rest. The door is free to turn about frictionless hinges along one edge. A person applies a constant force F = 120 N perpendicular to the door at the edge opposite from the hinges, so a distance of 2.0 m from the line along the hinges. The force remains perpendicular to the door as the door rotates. The door turns through 90° in 4.0 s. What is the moment of inertia of the door for an axis along the hinges?