Andrew K. answered • 07/01/19
MIT physics major
The force of friction is proportional to the normal force (the force on the box by the ramp that is perpendicular to the ramp). By drawing a force diagram and setting the net force in both the x and y directions equal to zero we can determine that the normal force equals m * g * cos(5) which equals 39.05 N. We can then multiply the normal force by the coefficient of friction to determine that the maximum force due to friction is 3.905 N. Note that this is the maximal force due to friction, but the force of friction can be less if the force acting on the block is less than 3.905. For example, is this scenario the force of friction is m * g * sin(5) which equal 3.42 N. This is because the force on the block going doing the ramp only equals 3.42 N, so the friction will only provide enough force to oppose the motion (if the force of friction was greater than the force down the ramp, the block would slide up the ramp which doesn't make sense).
