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如图,轻质金属导轨CD长2m,可绕C点转动,固定的均匀电阻杆AB与金属导轨CD平行,电阻杆AB每米阻值为10Ω,长度与CD一样。导轨D端通过绳子、滑轮与质量为3.5kg的重物M相连,一弹性轻质金属片垂直连接在AB、CD间且接触良好,并与质量为7kg的绝缘滑块Q粘连.已知:电源电压12V,灯泡规格“4V 1.6W”.闭合开关S,若滑块Q从C开始以0.2m/s的速度匀速向D运动,当M刚要离开地面时,灯L恰好正常发光.(不计导轨CD及滑片P的电阻,忽略温度对灯泡电阻的影响,忽略绳重,滑片P的弹力及一切摩擦,g取10N/kg)

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Walk For Charity

Dear Friend,

    Please join us for our annual Walk For Charity.Starting in Weldown,you and your friends can choose a delightful 10,20 or 30 kilometers' route.

    The money raised will provide support to help people all over the world.Start collecting your sponsors now and then simply come along on the day.Please read the instructions below carefully,especially if you require transport to and from Weldown.

    See you on Sunday 15 April.

    V Jessop: Walk coordinator

    PS.Well done to last year's walkers for helping to raise a grand total of £21,000.The money has already been used to build a children's playground.

    START TIME:

    30 km: 8-10 am      20 km: 8-10:30 am      10 km: 8-11:30 am

    The organizers reserve the right to refuse late-comers.

    CLOTHING should be suitable for the weather.If rain is forecast,bring some protection and be prepared for all possibilities.It is better to wear shoes that have been worn in,rather than ones that are new.

    ROUTE MAPS will be available from the registration point.The route will be sign-posted and arranged.Where the route runs along the road,walkers should keep to one side in single file,facing oncoming traffic at all times.If you need help along the route,please inform one of the staff.

    Free car parking is available in car parks and on streets in Weldown.

    BUSES:

    For the 10 and 20 kilometers' routes,a bus will be waiting at Fenton to take walkers back to Weldown.The bus will leave every half hour starting at midday.The service is free and there is no need to book.