问题 计算题

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S以及滑动变阻器R1的滑片P。前推操纵杆时轮椅前进,再向前时快速前进;拉操纵杆时,轮椅慢慢后退。又知蓄电池的电压U=24V(保持不变)、定值电阻R2=10Ω,电动机的额定功率P0=72W、额定电压U0=24V。

(1)从原理图可知,当开关S接到_________两个接线柱时,轮椅前进。

(2)当轮椅后退时,电流表示数为I=1A,此时电动机的实际功率为多少?

(3)当电动机以额定功率工作时,轮椅匀速前进的速度为1.5m/s,电动机线圈电阻损耗的功率为18W,求此时轮椅受到的阻力的大小。

答案

(1)3、4

(2)电阻R2的阻值为:U2=IR2=1A×10Ω=10V,电动机两端的电压为:U=U-U2=24V-10V=14V, 电动机的实际功率为:P=UI=14V×1A=14W;

(3)电动机的机械功率为P=P0-P线=72W-18W=54W,由于P=Fv,∴F===36N,匀速前进时:f=F=36N。

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     假设你是小伟。你的室友大明昨天接到你朋友Maria的电话。她正在研究中国的节日文化,需要你
的帮助。现在,请你根据大明所留的便条内容,给Maria回一封电子邮件。 
 
Xiaowei,
     Your friend Maria made a phone call to you yesterday. She wants to know the traditional
Chinese festival-the Lantern Festival. She wants you to tell her why we like it, when and how
we spend it (tell her at least 3 activities). Send an email to her at marial988@ gmail. com. Please
ask her what they do during Christmas for me.
                                                                                                                        Dawei
注意:
     1)电子邮件的格式和开头已给出,不计入总词数(80-100词);
     2)表达完整、书写规范、卷面整洁;
     3)提示词:sweet rice dumplings 汤圆 play with firecrackers 燃放鞭炮 the Lantern Festival 元宵节 
   
To: marial 988@gmail.com                                                                      From: xiaowei@sina.com
Subject: the Lantern Festival
Dear Maria,
     How are you? You asked me something about the traditional Chinese festival-the Lantern Festival. Actually, __________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
                                                                                                                                   Love
                                                                                                                                 Xiaowei
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