一细棒处于磁感应强度为B的匀强磁场中,棒与磁场垂直,与水平方向夹角为θ.磁感线水

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问题:

一细棒处于磁感应强度为B的匀强磁场中,棒与磁场垂直,与水平方向夹角为θ.磁感线水平指向纸内,如图11-42所示,棒上套一个可在其上滑动的带负电的小球C,小球质量为m,带电荷量为q,球与棒间动摩擦因数为μ,让小球从棒上端由静止下滑,求:

图11-42

(1) 小球的最大速度;

(2) 动摩擦因数μ应具备的条件.

考点:磁场对运动电荷的作用:洛伦兹力、左手定则
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“供应链管理”的英文缩写是

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魏晋以后,尚书机构内部组织承汉制而有增减,到______时称尚书省。( )

A.北魏

B.晋朝

C.南梁

D.北齐

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Section B

Hi Colin,

Glad to hear that you are going to have so many adventures in Africa. To make your trip more enjoyable, you should take some necessary things with you. You’ll need strong boots because you are going to  53  a lot.  54  is also necessary in case the weather is bad on Mount Kilimanjaro. A towel is also needed because you will get  55  when you go white-water rafting.

56  very important, too. You must take your tent, sleeping bags and so on. Also take a map of all the places  57  you will visit and a  58  so you don’t get lost. You will take some food and you’ll probably find water. Take care  59 , as you will need to take your water purifying tablets and place them in a pan when you boil the water. And remember to take a pocket knife to cut food or anything else when  60 .

Best wishes,

Jennifer

53. A. run                  B. ride                 C. drive               D. walk

54. A. A parka               B.A raincoat            C. An umbrella         D. A life jacket

55. A. hot                         B. excited              C. wet                D. cold

56. A. An equipment is                              B. Equipments are  

C. Equipment is                              D. The equipments are

57. A. where               B. that                 C. when              D. in which

58. A. compass              B. watch                C. candle                D. box of matches

59. A. although             B. though                     C. however            D. yet

60. A. needed                      B. cut                        C. asked               D. required

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关于旋转式压缩机说法正确的是()。

A.机壳内都是高压区

B.机壳内都是低压区

C.吸、排气同时进行

D.吸、排气先后进行

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婚飞

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