In a laboratory experiment on friction, a 135-N block resting on a rough horizontal table is pulled by a horizontal wire. The pull gradually increases until the block begins to move and continues to increase thereafter. Figure 5.52 shows a graph of the friction force on this block as a function of the pull.
(a) Identify the regions of the graph where static and kinetic friction occurs.
(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 be the coefficients of friction be in that case?

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fN) 5.0 500 25.0 PN) 250 500 750 100.0 125.0 1500