电动自行车是目前一种较为时尚的代步工具，某厂生产的一种电动自_爱下问搜题

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问题计算题

电动自行车是目前一种较为时尚的代步工具，某厂生产的一种电动自行车，设计质量(包括人)为m=80kg，动力电源选用能量存储为“36V 10Ah”(即输出电压为36伏，工作电流与工作时间的乘积为10安培小时)的蓄电池(不计内阻)，所用电动机的输入功率有两档，分别为P₁=120W和P₂=180W，考虑到传动摩擦以及电机发热等各种因素造成的损耗，电动自行车行驶时的功率为输入功率的80%，如果电动自行车在平直公路上行驶时所受阻力与行驶速率和自行车对地面的压力都成正比，即F_f= kmgv，其中k=5.0×10^-3s·m^－1，g取10m/s²。求：

（1）电动自行车在平直公路上能到达的最大速度；

（2）该电动自行车选用最高档行驶时，行驶的最长时间是多少小时？

（3）估算：选用“功率高档”时电动自行车在平直公路上的最大行程。

答案

（1）6m/s （2）2h （3）43.2km

1）当电动自行车以最大功率行驶且达匀速运动时速度最大，有

1 （3分）

P_实＝ηP₂＝F_fv_m （3分）

联立以上两式得：="6m/s " （3分）

（2）根据公式P=IU，可得高档电流为：I₂="5" A，（3分）

根据电池容量36×10×1=pt得：，得 t₂="2h " （3分）

（3）忽略电动自行车的启动和减速过程，可认为电动自行车能以最大速度行驶2 h，即：

s=v_mt₂="6×3600×2" m="43.2km " （3分）

单项选择题

牙髓活力温度测试的中冷刺激是指（）。

A.低于0℃的刺激

B.低于5℃的刺激

C.低于10℃的刺激

D.低于15℃的刺激

E.低于20℃的刺激

完形填空

One of my fondest memories as a child is going by the river and sitting idly on the bank. There I would   16  the peace and quiet, watch the water rush   17  and listen to the singing of birds and the rustling of   18  in the trees. I would also watch the bamboo trees   19  under pressure from the wind and watch them   20  gracefully to their original position after the wind had   21  .
When I think about the bamboo tree's ability to bounce back to its original position, the word "resilience" comes to mind. When used in   22  to a person this word means the ability to readily   23  from shock, depression or any other situation that stretches the limits of a person's   24  .
Have you ever felt like you are at your   25  point? Thankfully, you have survived the experience to live to talk about it.
During the   26  you probably felt a mix of emotions that threatened your health. You felt emotionally drained,   27  exhausted and you most likely stood   28   physical symptoms.
Life is a   29  of good times and bad times, happy moments and unhappy moments. The next time you are experiencing one of those bad times or unhappy   30   that take you close to your breaking point, bend,   31   don't break. Try your best not to let the situation get the best of you.
A   32  of hope will take you through the unpleasant ordeal (考验). With   33   for a better tomorrow or a better situation, things may not be as bad as they seem to be. The unpleasant ordeal may be easier to   34  if the final result is worth having.
If life gets   35  and you are at your breaking point, show resilience. Like the bamboo tree, bend, but don't break!

C．reference to

B．unreasonable

C．imagination