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Homework Statement
A 219-kg crate rests on a surface that is inclined above the horizontal at an angle of 20.1°. A horizontal force (magnitude = 501 N and parallel to the ground, not the incline) is required to start the crate moving down the incline. What is the coefficient of static friction between the crate and the incline?
Homework Equations
F=ma
The Attempt at a Solution
Made the coordinate system in the direction of the acceleration.
Drew FBD. FN in the +y direction. mgCOS20.1 in the -y direction.
Fx(501N) in the +x direction. mgSIN21.0 in the +x direction and Fk in the -x direction.
So,
Fy=may ---> a=0
FN=mgcos20.1
Fx=max
-Fk+Fx+mgsin20.1 = ma
-Fk+501N+770N=219(kg)a
-Ukmgcos20.1+1270N = 219(kg)a
-Uk2010(N)=219(kg)a-1270N
This is where I am stuck I am unable to solve for the kinetic coefficient because I have two variables. How do I get ax?