中考真题(2006·江苏连云港)在今年5月份助残活动中,某校初三同学为伤残军人买了一辆电动轮椅.同学们对这辆车的工作原理产生了兴趣.他们对照说明书的电路原理图(如图所示)了解到,操纵杆可操纵双刀双掷开关K以及滑动变阻器R_1的滑片P.前推操纵杆时轮椅前进,再向前推时快速前进;后拉操纵杆时轮椅慢慢 Zhongzao Zhenti (2006 · Lianyungang, Jiangsu Province) In the Paralympic activities in May this year, the first three students in a certain school bought an electric wheelchair for disabled soldiers, and the students were interested in the working principle of the car. The schematic (as shown) shows that the joystick controls the double-pole double-throw switch K and the slide P of the sliding rheostat R_1. The wheelchair is advanced when the joystick is pushed forward and quickly advanced when pushed forward; the pull-back joystick Wheelchair slowly