You are working in a shoe test laboratory measuring the coefficients of friction for running shoes on a variety of surfaces. The
shoes are pushed against the surface with a downward force of 400 N, and a sample of the surface material is then pulled out from under the shoe by a machine. The machine pulls with a force of 300 N before the material begins to slide. When the material is sliding, the machine only has to pull with a force of 200 N to keep the material moving. What is the coefficient of static friction between the shoe and the material
M = 600 kg u = 0 (as the car was at rest initially) v = 5 m/s Initial kinetic energy = ½mu² = ½×600×0 = 0 Final kinetic energy = ½mv² = ½×600×25 = 7500 J
