如图11所示，用绳索将重球挂在墙上，不考虑墙的摩擦。如果把绳的长度增加一些，则球对绳的拉力F1和球对墙的压力F2的变化情况是（）http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/fcfa14f39714448a954317de48b18c40.png
举一反三
- 如图所示，用绳索将重球挂在墙上，不考虑墙的摩擦。如果把绳的长度增加一些，则球对绳的拉力F1和球对墙的压力F2的变化情况是（） A: F增大，F减小 B: F减小，F增大 C: F和F都减小 D: F和F都增大
- 信号f1(t)和f2(t)如下图所示，f(t)=f1(t)*f2(t)，则f(-1)等于http://image.zhihuishu.com/zhs/onlineexam/ueditor/201906/0749958f4da44655959aea343dbe4d9c.bmp
- 如图9所示，建筑装修中，工人用质量为m的磨石对斜壁进行打磨，当时磨石加竖直向上大小为F的推力时，磨石恰好沿斜壁向上匀速运动，已知磨石与斜壁之间的动摩擦因数为 <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/8f90c371679b495faa8e0712ca86bd45.png" />，则磨石受到的摩擦力是（）<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/a9b96947560c4fb3b2d2878f99c076c1.png" /> A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/8ec695bac8e344da9c2dce17e053d2b7.png" /> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/75657b0b2e1f48328d47630c210769d2.png" /> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/8ff12bbcf235454885e8e28ee2735858.png" /> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/f2efc236752b455b87169561201d7b81.png" />
- 已知f1(t)和f2(t)波形如下，若f(t)=f1(t)*f2(t)，则f(0)=http://image.zhihuishu.com/zhs/onlineexam/ueditor/201906/e38151c6fa664a008f547dd1af821f92.bmp
- 设有一质点从A点作曲线运动到B点，如图1所示，A点和B点的位置矢量分别是 <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/0d76b5d4340c46fe8a8c4b8c35e04bde.png" />，则它们的大小之差<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/5ef37da7a8ec41729fdb08c5e0470007.png" />和它们的矢量差的大小<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/74f7e5aeb58746f990b78a02b130b693.png" />分别是（）<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/db95db190cf342bf902e99c4d8f76e6a.png" /> A: 2m，0 B: -1m，1m C: 0，0 D: 2m，2m E: 1m，1m F: 0，2m