The free body diagram of the crate can be shown as,
According to free body diagram, the net force acting on the crate is,
[tex]F=mg\sin \theta-f\ldots\ldots\text{ (1)}[/tex]The frictional force acting on the crate can be given as,
[tex]f=\mu N[/tex]According to free body diagram, the normal force acting on the crate is,
[tex]N=mg\cos \theta[/tex]Therefore, the frictional force becomes,
[tex]f=\mu mg\cos \theta[/tex]According to Newton's second law, the net force acting on the crate is,
[tex]F=ma[/tex]Therefore, equation (1) becomes,
[tex]\begin{gathered} ma=mg\sin \theta-\mu mg\cos \theta \\ a=g\sin \theta-\mu g\cos \theta \end{gathered}[/tex]Thus, the net acceleration of the crate can be expressed using Newton's second law as,
[tex]a=g\sin \theta-\mu\cos \theta[/tex]
