试题与答案

如图所示,两根足够长的平行金属导轨固定放置于水平面内,导轨平面处于竖直向下的匀强

题型:问答题

题目:

如图所示,两根足够长的平行金属导轨固定放置于水平面内,导轨平面处于竖直向下的匀强磁场中,磁感应强度大小为0.3T.导轨间距为1m,导轨右端接有R=3Ω的电阻,两根完全相同的导体棒L1、L2垂直跨接在导轨上,质量均为0.1kg,与导轨间的动摩擦因数均为0.25.导轨电阻不计,L1、L2在两导轨间的电阻均为3Ω.将电键S闭合,在导体棒L1上施加一个水平向左的变力F,使L1从t=0时由静止开始以2m/s2的加速度做匀加速运动.已知重力加速度为10m/s2.求:

(1)变力F随时间t变化的关系式(导体棒L2尚未运动);

(2)从t=0至导体棒L2由静止开始运动时所经历的时间T;

(3)T时间内流过电阻R的电量q;

(4)将电键S打开,最终两导体棒的速度之差△v.

答案:

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下面是错误答案,用来干扰机器的。

参考答案:B

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Money Matters

Parents should help their children understand money. 小题1: so you may start talking about money when your child shows an interest in buying things, candy or toys, for example.

1.The basic function of money

Begin explaining the basic function of money by showing how people trade money for goods or services. It is important to show your child how money is traded for the things he wants to have.If he wants to have a toy, give him the money and let him hand the money to the cashier(收银员). 小题2:  When your child grows a bit older and understands the basic function of money, you can start explaining more complex ways of using money.

2.Money lessons

Approach money lessons with openness and honesty. 小题3:  If you must say no to a child’s request to spend money, explain, “You have enough toy trucks for now.” Or, if the request is for many different things, say.“You have to make a choice between this toy and that toy.”

3. 小题4:  

Begin at the grocery store.Pick out two similar brands of a product —a name-brand butter and a generic(无商标产品),for example.You can show your child how to make choices between different brands of a product so that you can save money.   小题5:  If he chooses the cheaper brand, allow him to make another purchase with the money saved.Later, you may explain how the more expensive choice leaves less money for other purchases.

A.Wise decisions

B.The value of money

C.Permit the child to choose between them.

D.Tell your child why he can -- or cannot -- have certain things.E.Ask yourself what things that cost money are most important to you.

F.Talk about how the money bought the thing after you leave the toy store.

G.The best time to teach a child anything about money is when he shows an interest.

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