质量为m的质点，在有阻力的水平地面运动。设所受的牵引力F与速度呈正比，比例系数为k，已知阻力与重力成正比，且比例系数为u，研究其运动-Mass m particle resistance level of ground motion. Set suffered the traction F with speed proportional to the proportionality coefficient k, known resistance is proportional to the gr