题目

Washington D. C. is the capital of the United States. It’s the center of national government. It’s a busy, working city with a large population. But what is more, Washington is also a city of history and culture. Washington was created in 1790 when Congress ( the highest law-making body of the U. S. A. ) decided to place the nation’s new capital in the east of the country. It was build halfway between the northern and southern states of America. And of course it was named after George Washington, the first President of the United States. There are many tourist sights in Washington. Per飞机在水平跑道上加速滑行时受到机身重力mg、竖直向上的机翼升力F升、发动机推力F推、空气阻力F阻、地面支持力FN和轮胎与地面之间的摩擦力F摩。已知升力与阻力均与飞机运动的速度平方成正比，即F升=k1v2, F阻=k2v2，轮胎和地面之间的等效动摩擦因数为μ。假设飞机在跑道上加速滑行时发动机推力。（1）画出飞机在加速滑行时的受力分析图；（2）飞机在水平跑道上匀加速滑行所需条件是什么？（3）若飞机在水平跑道上从静止开始匀加速滑行后起飞，跑道的长度至少多大？