A professor's office door is 0.86 mm wide, 2.0 mm high, and 4.0 cmcm thick; has a mass of 25 kgkg ; and 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 5.5 N x m. What is the least force that you need to apply to the door to hold it open?

Afisherman notices that his boat is moving up and down periodically, owing to waves on the surface of the water. it takes a time of 2.70 s for the boat to travel from its highest point to its lowest, a total distance of 0.700 m. the fisherman sees that the wave crests are spaced a horizontal distance of 6.50 m apart. a. how fast are the waves traveling? b. what is the amplitude a of each wave?