高一下英语动词的时态.doc

-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- , as shown in the level of the ceiling of A fixed point A place A light bar, rod be vertical with the ceiling. The lower end of the rod with a light roller O. Another thread upper end fixed on the ceiling of the B point, thin lines across the pulley O, the bottom is a G weight of the object. BO long thin line with an Angle of theta ceiling = 30 o. System remain still, excluding all friction. In the following statement is correct () A. fine line BO tension size is on the ceiling B.a rod on the acting force of pulley size is C.a. rod and thread force size of pulley is G Da pole on the acting force of pulley size is G With heavy G as the research object, heavy G in only by the pull of gravity and thin line and balance, so thin line of pulling force and the gravity of weights in the weight back. Because thread without gravity, subject to all the friction, so the size of the tensile strength of the thin line for G everywhere, so A options thread BO is G to the tension size of the ceiling. With fine lines and pulley of the contact point as the research object, the contact point balance, has known two thread tension force and pulley upward force to the contact point of large reverse, such as drawing available pulley size upward force to the point of contact for G. With roller as the research object, pulley, only by a pressure rod and fine line contact, so C option error, should be 0. And a rod for the pulley should fine line to the reaction between the pulley and the power of the large reverse, such as is the G, so the D option is correct. -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- As shown, A and B are heavy, A by bypass small pulley P thread hanging, B in the rough level table; Pulley P is a diagonal short department on the ceiling of the O; Nodes are the three wires, pull a b b level objects, c pull springs along the vertical d