题干

下列说法中正确的是(   )

A:探究物体所受重力大小与物体的质量的关系时,物体密度是需要控制的变量

B:探究液体内部压强大小与液体的质量的关系时,液体密度是需要控制的变量

C:探究物体所受压力大小与物体所受重力大小的关系时,物体的受力面积是需要控制的变量

D:探究物体所受滑动摩擦力大小与物体所受重力大小的关系时,物体对接触面的压 力是需要控制的变量

上一题 下一题 0.0难度 选择题 更新时间:2012-10-26 04:20:36

答案(点此获取答案解析)

B,D

同类题4

    One terribly cold day, a snowstorm hit our area. Needing firewood, I quickly set out with my best friend, Bruce, to look for a tree to cut down. Cutting down a tree in a snowstorm can be dangerous. ① So to have a friend who could warn me of dangerso was important.
    When I chose a big 23-meter-tall tree and prepared to cut it down, Bruce suddenly warned me, “Don't cut down that tree! It's too close to the power line!” I wasn't sure about it. So I decided to disregard his warning. I couldn't wait to finish the job and go back home. I began cutting down the tree.② When the tree fell, there was no longer any doubt whether my friend was right.
    The tree caught the power line, bringing it to the ground. I considered cutting the tree off the line. After all, electricity can't travel through wood. As I reached out my finger to touch the tree, pain ran up my arm and through my head. I had been shocked!
    After I returned home and told my mother what happened, she quickly called the power company. Workers from the power company soon arrived. One of them asked if I had touched the tree, and when I told him I had, his face turned pale. “You should have been killed,” he said. It was my boots that saved my life.
    ③Within two hours, the workers removed the tree. Soon the snowstorm calmed down——but not my mother. Even though she was glad that I wasn't hurt, my mother was still serious with me. After all(毕竟), I shouldn't have brushed off my friend's warning.