题目

在探究合力的方法时，先将橡皮条的一端固定在水平木板上，另一端系上带有绳套的两根细绳．实验时，需要两次拉伸橡皮条，一次是通过两细绳用两个弹簧秤互成角度地拉橡皮条，另一次是用一个弹簧秤通过细绳拉橡皮条．                                                                                                                                               ①实验对两次拉伸橡皮条的要求中，下列哪些说法是正确的                    （填字母代号）                  A．将橡皮条拉伸相同长度即可                                                                                        B．将橡皮条沿相同方向拉到相同长度                                                                              C．将弹簧秤都拉伸到相同刻度                                                                                        D．将橡皮条和绳的结点拉到相同位置                                                                             ②同学们在操作过程中有如下议论，其中对减小实验误差有益的说法是             （填字母代号）                      A．两细绳必须等长                                                                                                          B．弹簧秤、细绳、橡皮条都应与木板平行                                                                       C．用两弹簧秤同时拉细绳时两弹簧秤示数之差应尽可能大                                              D．拉橡皮条的细绳要长些，标记同一细绳方向的两点要远些．                                                                                                                                                                               答案：①BD  ②BD

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