问题 计算题

如图甲所示,两根质量均为m=0.1kg完全相同的导体棒a、b,用绝缘轻杆相连置于由金属导轨PQ、MN架设的斜面上。已知斜面倾角θ=530,a、b导体棒的间距是PQ和MN导轨间距的一半,导轨间分界线OO'以下有方向垂直斜面向上的匀强磁场。当a、b导体棒沿导轨下滑时,其速度v与时间t的关系如图乙所示。若a、b导体棒接入电路的电阻均为R=1Ω,其它电阻不计。(取g=10m/s2,sin53°=0.8,cos53°=0.6)

(1)依据v-t图像,求b导体棒匀速运动阶段的位移大小;

(2)求a、b导体棒与导轨间的动摩擦因数μ;

(3)求匀强磁场的磁感应强度B大小。

答案

解:(1)由图乙可知导体棒b刚进入磁场时a、b的连接体做匀速运动,

当导体棒a 进入磁场后才再次加速运动,因而b棒匀速运动的位移即为a、b棒的间距,

依题意可得:s=vt=0.6m。

(2)设导体棒运动的加速度为a,由图乙得:

由牛顿第二定律得:

(3)当b导体棒进入磁场时,连接体做匀速运动时

d=2s

联立解得=

阅读理解

阅读理解。

     Among the many things that Brisbane (布里斯班), Australia, does really well, the care for kids is the

best one. Here is a list of places that will be suitable for your kids.

     Swimming pools

     Simple way for happiness: mix kids with water. Of course, this is a choice for the hot summer months.

     Parks

     Free outdoor fun: it's suitable for kids of all ages. It's a place for parents to let kids run wild.

     The Children's Art Centre

     The Children's Art Centre has been very popular. Kids' favorite here is some exhibitions specially designed

for children. But we must pay some money.

      South Bank Parklands

      South Bank Parklands has everything you need to keep kids amused. Take them for a swim at the man-

made beach. On weekends, go through the arts market or go to a cheap movie. South Bank Parklands often

gives free performances too.

     Roma Street Parkland

     Close to bus transport, this parkland is easily accessible (可进入的). It's ideal (理想的) for kids of all ages.

Younger kids can take a trip on the Jelly Bean Express, a 1.3 km trackless train ride around the parkland. Free

entry and open every day.

1. What does the text mainly talk about? [ ]

A. Brisbane-a beautiful city in Australia.

B. How to travel in Brisbane.

C. Famous parks and activities in Brisbane.

D. Some interesting places for kids in Brisbane.

2. If your kids want to watch performances for free, you can take them to _____. [ ]

A. South Bank Parklands

B. Roma Street Parkland

C. The Children's Art Centre

D. Parks

3. What can we know about Roma Street Parkland? [ ]

A. It opens only at weekends.

B. Only younger kids can visit it.

C. We need not buy tickets for a visit.

D. Younger kids have to walk while visiting it.

4. What do kids love best in the Children's Art Centre? [ ]

A. Man-made beach.

B. Some exhibitions.

C. Arts market.

D. Jelly Bean Express.

5. Who will be interested in the text most? [ ]

A. Children and parents.

B. Artists

C. Movie lovers.

D. Swimmers.

多项选择题