题目

Is there intelligent (有智力的) life on other planets? For years, scientists said “no. or “we don't know. But today this is changing. Seth Shostak and Alexandra Barnett are astronomers(天文学家). They believe intelligent life exists (存在) somewhere in the universe. They also think we will soon contact these beings(人：生物).Why do Shostak and Barnett think intelligent life exists on other planets? The first reason is time. Scientists believe the universe is about 12 billion years old. This is long enough for other planets to have intelligent life, say Shostak and Barnett. Th10．如图1所示，打点计时器固定在斜面的某处，让一滑块拖着穿过打点计时器的纸带从斜面上滑下．图2是某同学验时打出的某条纸带的一段．已知打点计时器使用的交流电频率为50Hz，利用该纸带中测出的数据可得滑块下滑的加速度大小a=4.00 m/s2．为了测出滑块与斜面间的摩擦力，该同学已经测出斜面的长度l及高度h，他还需要测量的物理量是滑块的质量m，利用测得的量及加速度a表示摩擦力的大小f=mg$\frac{h}{l}$-ma．