一个物体做自由落体运动，则在物体下落的过程中（ ）
A．物体第2s末的速度为10m/s
B．物体第2s内的平均速度为10m/s
C．物体前2s内下落的高度为20m
D．物体第2s内下落的高度是10m
A、根据速度时间公式得：v=gt=20m/s，故A错误；
B、根据根据
=. v
求得：v1+v2 2
=. v
m/s=15m/s 故B错误；10+20 2
C、根据位移时间公式得：h=
gt2=1 2
×10×4m=20m，故C正确；1 2
D、由B得第二秒内的平均速度为15m/s，根据h=
t得：h=15×1m=15m，故D错误．. v
故选C．
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| One can have many experiences, but the one I never forget is my bicycling trip in Taiwan. When we were going to 1 school,my teacher suggested that we could do something special to remember our school life. After a long discussion,we decided to travel 2 the whole island by bicycle. We began to get some training to make our 3 stronger. So we ran 3,000 meters after school. At first, I could only run about 2,000 meters. My legs were heavy like steel and my heart 4 very fast. After two weeks of training, I could run 3,000 meters 5 . We started our journey (旅行) the last week of July. We rode about 100 kilometers 6 . It was very hot and our clothes were 7 all the time. One day, we were riding up the mountain when there was 8 wrong with my bicycle, and I fell and was hurt. I almost gave up and didn't want to 9 the trip, but I tried to solve the problems successfully and kept on. Fifteen days passed, we returned to school again. We were so 10 . This experience was like a miracle (奇迹) for me. I learned that I could do what I want to. | ||||
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