Problem: There's an office door, 0.86m wide, 2.0m high and 4.0cm thick. It pivots on frictionless hinges. A "door closer" is attached to the door and the top of the door frame. When the door is open and at rest, the door closer exerts a torque of 4.7Nm.
Part A: What is the least force that you need to apply to hold the door open?
I need help to find the least force that you need to apply to hold the door open.