利用牛顿第二定律可以测定物体的质量，1966年曾在太空中完成了以牛顿第二定律为基础的测定质量的实验，如图所示，实验时，用“双子星号”宇宙飞船m₁去接触正在轨道上运行的火箭组m₂（发动机已熄火），接触后开动飞船尾部的推进器使飞船和火箭组共同加速．推进器的平均推力F=895N，推进器开动7s，测出火箭和飞船这个联合体的速度改变量是△v=0.91m/s．已知“双子星号”宇宙飞船的质量m₁=3400kg．问

Dunnottar Castle (城堡)

    Castle open times:

    Summer season: (April 1^st - September 30^th ) 9:00-5:30 every day.

    Winter season: (October 1^st -March 31^st )

    Oct 1^st - Oct 28^th 10:00-4:30

    Oct 29^th -Nov 11^th 10:00-3:30

    Nov 12^th -Nov 25^th 10:00-3:00

    Nov 26^th- Jan 20^th 10:00-2:30

    Jan 21th-Feb 3^rd 10:00-3:00

    Feb 4^th- Feb 17^th 10:00-3:30

    Feb 18^th- Feb 24^th 10:00-4:00

    Feb 25^th- Mar 31^st 10:00-4:30

    Bad Weather Conditions:

    Before going to the Castle, we advise you to visit our website(www. dunnottar.com)to make sure that the Castle is open. On the days of bad weather, the castle may be closed for safety reasons.

    Prices:

    Adult ticket:

    Children ticket:

    Guide Book:

    Buy tickets at the door.

    We do not offer pre-booking(预定)for tickets.

    Castle Closure Dates:

    The Castle will be closed on the following dates-25th of December and the 1^st 2^nd of January.

    Post code: AB39 2TL

    Dogs: Dogs are welcome at the Castle as long as they are kept on a leash(皮带) at all times.

16-18世纪，在美洲大陆出现了许多被称为新西班牙、新法兰西、新奥尔良、新尼德兰、新英格兰的地名，这些地名的出现是因为（    ）

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