题干

在用如图所示的装置做“探究功与速度变化的关系”实验时,下列说法正确的是(   )

A:为了平衡摩擦力,实验中可以将长木板的左端适当垫高,使小车拉着穿过打点计时器的纸带自由下滑时能保持匀速运动

B:可以通过改变橡皮筋的条数来改变拉力做功的数值

C:可以通过改变小车的质量来改变拉力做功的数值

D:实验中要先释放小车再接通打点计时器的电源

E:通过打点计时器打下的纸带来测定小车加速过程中获得的最大速度

F:通过打点计时器打下的纸带来测定小车加速过程中获得的平均速度

上一题 下一题 0.0难度 选择题 更新时间:2018-01-23 11:03:39

答案(点此获取答案解析)

A,B,E

同类题4

      You either have it, or you don’t-a sense of direction. But why is it that some people could find their way across the Sahara without a map while others can lose themselves in the next street?
     Scientists say we’re all born with a sense of direction, but it is not properly understood how it works. One theory is that people with a good sense of direction have simply worked harder at developing it. Research being carried out at Liverpool University supports this idea and suggests that if we don’t use it, we lose it.
   “Children as young as seven have the ability to find their way around,” says Jim Martland, research director of the project. “However, if they are not allowed out alone or are taken everywhere by car, they never develop the skills.”
Jim Martland also emphasizes that young people should be taught certain skills to improve their sense of direction. He makes the following suggestions:
    If you are using a map, turn it so that it relates to(与……有联系) the way you are facing.
   If you leave your bike in a strange place, put it near something like a big stone or a tree-something easy to recognize. Note landmarks on the route as you go away from your bike. When you return, go back along the same route.
   Simplify(简化) the way for finding your direction by using lines such as streets in a town, streams, or wells in the countryside to guide you. Count your steps so that you know how far you have gone and note any landmarks such as towerblocks or hills which can help to find out where you are.
   Now you will never get lost again!