问题 单项选择题

如图是甲、乙两物体做直线运动的v一t图象.下列表述正确的是()

A.乙做匀加速直线运动

B.0~1s内甲和乙的位移相等

C.甲和乙的加速度方向相同

D.甲的加速度比乙的小

答案

参考答案:A

解析:在速度时间图象中,某一点代表此时刻的瞬时速度,时间轴上方速度是正数,时间轴下方速度是负数;切线代表该时刻的加速度,向右上方倾斜,加速度为正,向右下方倾斜加速度为负;图象与坐标轴围成面积代表位移,时间轴上方位移为正,时间轴下方位移为负。

阅读理解

阅读理解。

    Have you ever seen a horse with toes (脚趾)? Millions of years ago, horses had many toes. They had

four toes on each front foot. They had three toes on each back foot. The horses were smaller than cats.

    These small horses lived in the forest. Their many toes helped the horses run over the soft wet ground. 

    It was very hot in the forest. But the weather changed. It became cold. Many trees couldn't live in cold

weather. The trees died and fell. Open field took the place of (代替) forests. The sun made the ground dry

and hard (坚硬). 

    Horses began to change too. They began to get bigger. This took a long time. On the dry hard land,

horses needed only their middle toes for running. Their middle toes became hard. After a long time horses

had only one hard toe on each foot. We call this hard toe a hoof (马蹄).

1. Long ago, the horse had four toes on each of its ______. [ ]

A. back feet

B. front feet

C. right feet

2. The cats were ______ the horses at that time. [ ]

A. much bigger

B. smaller than

C. bigger than

3. Which of the three sentences is true? [ ]

A. The weather stays the same the whole year all over the world.

B. When the weather changed, animals began to change too.

C. Cats were bigger in the past than they are today.

4. On the dry hard land ______. [ ]

A. horses needed a lot of room for running

B. a horse needed more than four toes for running

C. horses needed only their middle toes for running

5. Now each horse has ______ on its feet. [ ]

A. one toe

B. three toes

C. four toes

多项选择题