质点的运动学方程为x=3t, y=4t2,它在t时刻的速度矢量为
A:
B:
C:
D:
A:
B:
C:
D:
举一反三
- l-矩阵<img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/202008/500186eca47a45dfbdb56b3f454593c8.png" />的Smith标准形为()。 A: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/202008/29463535c69144b08617f313e85b7d59.png" /> B: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/202008/be82c74bd5e6499b9c4bd798f704df00.png" /> C: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/202008/509e3bfd1b114727974787c7f1dab1a9.png" /> D: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/202008/777d67f69e83438f95215aa7434519d5.png" />
- 劳动（L）的总产量下降时( ） A: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/202008/76b56ea415c443cca8a15904fc96c163.png" /> B: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/202008/1d3a1a6edbbf48829cf2b8219bcee903.png" /> C: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/202008/8b96eb0faabc4175aacb9c02aaedc8a3.png" /> D: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/202008/4509f4a8c33a4321befc1ad8d4f56d1d.png" />
- 下列化合物命名正确的是： A: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/202008/7edd2de514754adebb8fd41f2e3745b9.png" /> B: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/202008/87e72f99416449fd8aeac22844518d5c.png" /> C: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/202008/bc9cd89438694bdbbc585f1eea17dced.png" /> D: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/202008/3a5edc8ac0ab4b97b781f76c36e1d75e.png" />
- 通电延时时间继电器的线圈图形符号为（）。 A: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/202008/783d4e013daa4f7384730ae4c5a54005.png" /> B: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/202008/401007c00c3d4e8badd1c54da42a55a9.png" /> C: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/202008/ac90a5663c3c4f51b28a33db3803f091.png" /> D: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/202008/e66d824c1ee2489db43385dfe2e35599.png" />
- 延时断开常闭触点的图形符号是（）。 A: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/202008/d0440f2b1f0c44d8ac0c20659a545afb.png" /> B: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/202008/b530bc5c319048d9a65e2b535dbd67f0.png" /> C: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/202008/0012e78e5b7543b48df5d96c1404d697.png" /> D: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/202008/906ec1ecfa32479ea47371c74c431dca.png" />