问题 计算题

如图甲所示,放在水平桌面上的两条光滑导轨间的距离为L=1m,质量m=1kg的光滑导体棒放在导轨上,导轨左端与电阻R=4W的电阻相连,其它电阻不计,导轨所在位置有磁感应强度为B=2T的匀强磁场,磁场的方向垂直导轨平面向下,现在给导体棒施加一个水平向右的恒定拉力F,并每隔0.2s测量一次导体棒的速度,乙图是根据所测数据描绘出导体棒的v-t图像,(设导轨足够长)求:

(1)力F的大小;

(2)t=1.6s时,导体棒的加速度;

(3)估算1.6s电阻上产生的热量。

答案

解:(1)由图像可知:v=10m/s时,安培力等于拉力F

E=BLV

I=E/R,F=F=BIL=10N

(2)由图像可知,时间t=1.6s时导体棒的速度vˊ=8m/s,此时导体棒上电动势E=BLvˊ

导体棒受到的安培力:

由牛顿第二定律得:F-Fˊ=ma,a=2m/s2

(3)根据动能定理:

由图像可知:位移l为t=1.6s和v-t图线及坐标轴所包围的面积,即l=40×1×0.2m=8m

所以

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PENRICE

COMMUNITY COLLEGE

Cornwall County Counicl

We Need Two

ASSISANT HEADTEACHERS

From January 2006

L13—17(£44,703—£49,314)

Penrice Community College is a highly regarded and successful 11-16 specialist languages college. Following the recent appointment of a new headteacher  we’re restructuring the leadership team to create two new roles.

One post will involve leading teaching teams with responsibility for developing curricula(课程) and time-tabling.

The other post will be leading student based teams and responsibility for student learing outcomes and the removal of barriers to student success such as poor attendance or disaffection.

Penrice Community College is:

·A school with 1,350 wonderful students

·High achieving with results well above average

·Mentioned twice in HMCl’s outstanding schools list

·A British Council International School

·Situated in a beautiful part of mid-Cornwall

All enquires for information and application packs should be made to Danielle Eyres on 01726—72613 or at secretary@penricornmvall .sch.uk

Closing date for applications is Tuesday October 4th at noon. Interviews will be held on Monday 17th and Tuesday 18th October 2005.

45.The underlined word “restructuring’ probably means ________.

A.formally telling sb to do            B.Joining the two parts together

C.rebuilding sth and making it work again    D.extending the size of sth

46.The purpose of the above passage is to ________

A.introduce the advantages of a school  

B.report the appointment of a new head teacher

C.call on more students to go to school  

D.advertise for new assistant headteachers

47.The two new posts are required to do all the following EXCEPT ________.

A.stop students missing classes                     B.get students interested in learning

C.lead students-based teams                         D.arrange new curricula

48.HMCI is probably the name of ________.

A.an educational organization                      B.a school leader

C.a political party                                      D.a news reporter