题目

吊车以2m/s的速度将重物1×105N匀速向上提起，这时钢索对重物的拉力是N； 若钢索改为以3m/s的速度使重物匀速下降，此时钢索对重物的拉力大小是N，方向. 答案：【1】1×105【2】1×105【3】竖直向上补全对话根据对话内容，从方框内的选项中选出能填人空白处的最佳选项，其中有两个选项为多余选项。A：It's very late．Are you still on the computer?B：Well，yes． 1.A：What kind of e—mails?B：Some are messages from my teacher and some are from my friends．A：Do you have to write them back right away?B：2. ．Usually people want a quick reply．A： 3. ．B：I've already had 50 people's address in my address book! And 4.A： 5. ．E—mail is really very convenient(方便的)．A．I think e—mail is one of the best ways to communicate with others．B．I've got so many e—mails to go through．C．I agree Will you．D．Of course!E．How many e—mails addresses have you had?F．I feel like playing computer games．G．I am not sure whether I'm right or wrong．