1-3物理练习（1-3 physical exercises）.docVIP

1-3物理练习（1-3 physical exercises） The first chapter of third hours A choice (10 items, each item of 6 points, a total of 60 points, the four options for each question there are at least one with students, all selected for the 6 points, failed to choose 3 points, 0 points the wrong) 1. hand light bar, the other end of the rod is provided with a small pulley support C, hanging heavy rope, as shown in the figure, is to maintain the C of the pulley position unchanged, the rod downward turning an angle lever force on the pulley C (will) A. B. constant C. small D. cannot be determined [analysis] force on force rod C of the pulley rope is equal to two, because the two rope force constant, constant force on the rod block C. Answer [B] 2. as shown on the right, an object by bypassing the fixed pulley rope pulling, three cases were shown to hold, in these three cases, if the tension in the rope are respectively F1, F2, F3, axis of fixed pulley support are respectively FN1, FN2, FN3. the friction pulley, regardless of quality, is () A.F1 = F2 = F3, FN1FN2FN3 B.F1F2F3, FN1 = FN2 = FN3 C.F1 = F2 = F3, FN1 = FN2 = FN3 D.F1F2F3, FN1FN2FN3 [analysis] because of the fixed pulley only changes the direction of the force, do not change the size of the force, so F1 = F2 = F3 = G, and the axis of the fixed pulley support force is equal to the rope to the fixed pulley force. And the two known component of the size of the resultant force meet the relation and the angle between the two component: F = = G, theta is larger, the smaller the F, the FN1FN2FN3 A, the only option is correct. Answer [A] 3. schematic diagram of the safety net to figure a is shown acrobatics, structure for Affirmative net lattice, O, a, B, C, D... Etc. as network nodes. Rope safety net horizontal tension, if the quality of M players and falling from a height, fell at O. The concave to the lowest point, dOe and bOg were a net rope angle upward 120 degrees, as shown in Figure B, at O point of impact force down the size o