Static Friction and inclined planes (1 Viewer)

[donrob15]

I have half yearly exams coming up and my engineering studies techer has gone away for holidays!

I need to know how to do a type of question on friction and the inclined plane that is in R.K. MULLINS Engineering Mechanics: Assignment 8 (chapter 11) Page163 Question 12:

100 kg box on a 2in6 (18.43 degrees) inclined plane. A force that is inclined at 25 degrees to the plane (43.43 degrees to the horizontal) is just preventing the box from sliding, therefore friction is acting up the plane. coeficient of friction = 0.1. Find the force.

not sure if i am meant to post questions but i am having a lot of difficulty and this is a last resort. i can do most of the other questions easily.

help will be greatly appreciated.

 

[withoutaface]

Find the normal force, which is going to be mgsin(theta), where theta is the angle of the incline, and m is the mass of the box. Then you find the total static friction which will be mu*N, which is equal to 0.1*mgsin(theta). You then split all the forces up into components, and equate everything to zero.

 

[donrob15]

The normal force is not equal to mgsin(theta) as the holding force, which is just holding the box from sliding, is inclined to the plane itself, therfore the normal reaction will be less than the perpendicular component of the weight force.