问题 选择题

下列说法中正确的是(  )

A.静止的物体也可以受到滑动摩擦力的作用;摩擦力都与正压力成正比

B.有摩擦力存在时一定有弹力,有弹力存在时不一定有摩擦力

C.由于月球的重力加速度是地球的1/6,所以,同一物体从地球搬到月球表面,其惯性减小5/6

D.使静止在地面上的物体动起来比维持该物体运动所需的力更大,所以物体静止时的惯性比运动时大

答案

A、静止的物体也可以受到滑动摩擦力的作用,比如:正在地面上滑行的物体,地面受到滑动摩擦力,但滑动摩擦力总是随物体间的压力的增大而增大,而静摩擦力与压力无关.故A错误.

    B、有摩擦力存在时一定有弹力,有弹力存在时,若没有相对运动趋势或相对运动,则没有摩擦力.故B正确.

    C、同一物体从地球搬到月球表面,虽然月球的重力加速度是地球的1/6,但是质量没变,所以惯性也不变,故C错误.

    D、使静止在地面上的物体动起来比维持该物体运动所需的力更大,是因为最大静摩擦力比滑动摩擦力大,而惯性大小与运动状态无关.故D错误.

故选B

完形填空

  小题1:   I like it because although it’s hard work, every day is different! It all depends on what is wrong with the animals that come in.

At my clinic(诊所), I work long days on Mondays, Wednesdays and Fridays, and short days on Tuesdays, Thursdays and Saturdays. Sunday is my day off so I can spend some time with my family.

   小题2:   My clerk opens the door, turns on some music, and makes everyone a cup of tea or coffee. My assistant cleans and feeds the animals. The phones start to ring and people make appointments. This is a very busy time of day!

At 9 am, pet owners start to arrive with their sick pets. Appointments take up the whole morning.    小题3:   I don’t examine(检查)any new sick animals. I use these two hours to have lunch and do all my paperwork.

At 2 pm. I start to see sick animals again. At 5 pm, three students from a local school who love animals arrive to help out.    小题4:   I am always happy to see their smiling faces!

From 5 pm to 7pm, I continue to see sick animals. Then, at 7 pm, we close our doors and the clean-up begins! We tidy the clinic, and feed and clean the animals. Of course,we also stroke(轻抚)them and give them hugs! Then, we turn off the lights and go home.    小题5:  

I’m very happy being a vet, though unexpected things sometimes happen!

A.Do you like pets?

B.It is fun being a vet.

C.At midday, I stop for two hours.

D.Animals are not easy to deal with.E. My day at my clinic begins at 7 am.

F. This is the type of day I want to have.

G. They are very kind and warm-hearted.

填空题