问题 实验题

某同学设计了如图所示的装置,利用米尺、轻绳、轻滑轮、轨道、滑块、光电门、托盘天平和砝码等器材来测定滑块和轨道间的动摩擦因数μ。导轨上A处有一质量为M的滑块,滑块上装有宽度为b的遮光片,滑块和托盘上分别放有若干砝码,滑块上砝码总质量为m′,托盘和盘中砝码的总质量为m。导轨上B处有一光电门,可以测出遮光片经过光电门时的挡光时间Δt。实验中,滑块在水平轨道上从A到B做初速为零的匀加速直线运动,重力加速度g取10m/s2

小题1:若测得AB距离为x,则计算滑块加速度a的运动学公式是 ▲  

小题2:根据牛顿运动定律得到a与m的关系为:,他想通过多次改变m,测出相应的a值,并利用上式来计算。若要求保证a是m的一次函数,必须使保持不变,实验中应如何操作? ▲  

小题3:实验得到a与m的关系如下表所示,作出a—m图像,并根据图像求得μ=  ▲ (取两位有效数字)

a/m·s20.190.230.270.320.350.39
m/10-2kg636465666768
5u

答案

小题1:

小题2:把砝码盘中的砝码放到滑块上(或把滑块上的砝码放到砝码盘上)

小题3:μ=0.23(在0.21~0 25范围内均给满分)

小题1:滑块在水平轨道上从A到B做初速为零的匀加速直线运动,根据

小题2:对整体进行研究,根据牛顿第二定律得:若要求a是m的一次函数必须使m不变,即使m+m′不变,在增大m时等量减小m′,

所以实验中应将从托盘中取出的砝码置于滑块上.

小题3:将取为k,有k==,在图象上取两点将坐标代入

解得μ=0.23(在0.21到0.25之间是正确的)

完形填空

First Job Search Tips

Keep in mind that you may not get the first job you apply for, or the second... A job search can take time, especially if you don't have much experience. Here's how to ensure you're a top-notch candidate for the jobs you are applying for.

Be Persistent. Wait a few days, then follow-up your application with a phone call to the hiring manager reiterating your interest. If you have applied in person, stop in again and mention that you are really interested in the opportunity.

Don't Stop. Don't apply at one place and wait for the phone to ring. Complete as many job applications as you can, and consider a variety of positions.  小题1:   .

  小题2:   . Applicants who are only available for limited hours are less likely to get hired than those who are flexible as to when they can work. For example, one candidate for a summer job told the employer that they were only available on Wednesday afternoons and Saturday mornings. Compare that to another applicant who selected "any" on the Hours Available section of the job applicant and you can see why the second applicant got the job.

Use Your Connections.  小题3:    . Does your mom shop regularly at the store where you'd like to work? If so, have her mention that you're looking for a job. That's how I got my first job and how my brother got his first job at the drug store across the street.

Dress Appropriately. When applying for jobs, dress as though you had the job. If you're applying for a retail position, for example, visit the store before you apply to see what the staff is wearing.

  小题4:    . When in doubt, dress up, not down.

Don't Give Up. Job searching isn't easy, especially when you don't have much experience or many skills.  小题5:    . Your first job will be a stepping stone to your next job - and to your future career.

A.Don’t stop to look for a job.

B.The more you apply, the better chance you have of finding a job.

C.Be Flexible.

D.It will give you an idea as to how you should dress.E.You shouldn’t apply for different jobs at the same time.

F.If you have a connection, use it.

G. Keep trying and keep applying and you will find a job.

单项选择题