1. The problem statement, all variables and given/known data a block of mass 2kg is in at rest on a rough plane inclined at 30°, it is in limiting equilibrium with with a force of 20N applied horizontally (to the ground). Find the coefficient of static friction between the block and the plane. 3. The attempt at a solution [itex] R=mgcos30+20sin30\\ .\\ mgsin30-μR=20cos30\\ mgsin30-μmgcos30+μ20sin30=20cos30\\ 9.8-16.97μ+10μ=17.32\\ 9.8-26.97μ=17.32\\ -26.97μ=7.52\\ μ=-0.28\\ [/itex] Now I now my answer cannot be minus something as 0<μ<1, however, I am unsure as to whether it is my understanding of the question or the algebra I have got wrong. Im sure its a silly mistake, it usually is with me but any help or advice is greatly appreciated.