题目

阅读理解 When it comes to generation gap (代沟), we usually think of different tastes in music, or pastimes. But now the generation gap is handwriting. After one teacher in Tennessee discovered that she had students who couldn't read what she was writing on the board, she posted it on the Internet saying that handwriting should be taught in schools. Others who are against it claim that handwriting has become out of time in our modern world. Typed words have become a main form of communication. Once a practical skill, handwriting is no longer used by most of Americans. It is no longer tau13．若有一飞行器P绕月球做匀速圆周运动，周期为T，月球相对飞行器的张角为θ，求月球的平均密度（万有引力常量为G）