3. A block with a force of the Earth of -300. N is moved at constant velocity over a horizontal surface by a force of +50.0 N applied parallel to the surface. What is the coefficient of kinetic friction?

At 20∘c, the hole in an aluminum ring is 2.800 cm in diameter. you need to slip this ring over a steel shaft that has a room-temperature diameter of 2.804 cm . 1. to what common temperature should the ring and the shaft be heated so that the ring will just fit onto the shaft? coefficients of linear thermal expansion of steel and aluminum are 12×10−6 k−1 and23×10−6 k−1 respectively.