5.26 . In a laboratory experiment on friction, a 135-N block rest- ing on a rough horizontal table is pulled by a horizontal wire. The pull gradually increases until the block begins to move and contin- ues to increase thereafter. Figure E5.26 shows a graph of the fric- tion force on this block as a function of the pull. (a) Identify the

5.26  . In a laboratory experiment on friction, a 135-N block rest- ing on a rough horizontal table is pulled by a horizontal wire. The pull gradually increases until the block begins to move and contin- ues to increase thereafter. Figure E5.26 shows a graph of the fric- tion force on this block as a function of the pull. (a) Identify the regions of the graph where static and kinetic friction occur. (b) Find the coefficients of static and kinetic friction between the block and the table. (c) Why does the graph slant upward in the first part but then level out? (d) What would the graph look like if a 135-N brick were placed on the box, and what would the coefficients of friction be in that case?