Grade 12th passMechanics
A student attaches a ruler to a block of wood sitting on a horizontal surface as shown in Fig. 3-20a. The surface exerts a large frictional force on the block. A nail is fastened at the 0-in, mark. The student pulls the rubber band tight at the 5-in . mark; he then pulls it tighter and when it reaches the 8-in. mark, the block of wood just starts to move (Fig. 3-20b). Before the block begins to move, the net force on the block when the rubber band is stretched 7 in. is
(A) greater than (B) equal to
(C) less than
(D) unrelated to the net force on the block when the rubber band is stretched 6 in.
