Q1. A professor's office door is 0.85 wide, 2.0 high, and 4.0 thick; has the mass of 25; and pivots on frictionless hinges. A "door closer" is attached to door and top of the door frame. When the door is open and at rest, the door closer exerts a torque of 5.20. What is the least force that you want to apply to the door to hold it open?
Q2. A 426 kg bear grasping a vertical tree slides down at constant velocity. The acceleration of gravity is 10m/s2. What is the friction force that acts on the bear? Answer in units of N.
A 29 kg chair initially at rest on a horizontal floor requires a 365 N horizontal force to set it in motion. Once the chair is in motion, a 325 N horizontal force keeps it moving at a constant velocity. The acceleration of gravity is 9.81 m/s2 .
a) What is the coefficient of static friction between chair and floor?
b) What is the coefficient of kinetic friction between chair and floor?