A worker stands still on a roof sloped at an angle of 36 degrees above the horizontal. He is prevented from slipping by a static frictional force of 390 N. Find the mass of the worker.
(Every example of this in the book gives the Coefficient of static friction in the problem, so i am confused on how to find this guys mass with just the static friction. please explain a little if you could so ill understand, so ill know for other problems or tests....thanks in advance!
isn't the normal force the weight of the object and to find the normal force you use the relationship between the frictions, the normal, and the coefficient. Also because its 36 degrees you are going to have to factor in the angle against the weight of the person. At least this is how I think you solve the problem with that data given.
http://en.wikibooks.org/wiki/Physics_Study_Guide/Normal_force_and_friction this should help a little with the relation.