题目

某人造地球卫星绕地球做匀速圆周运动，其轨道半径为地球半径R的3倍，已知地面附近的重力加速度为g，引力常量为G，求这颗人造地球卫星的向心加速度和周期． 答案：=g．     T=6    (2分) 解析: 解：设地球的质量为Ｍ，人造地球卫星的质量为m，由万有引力定律有       G=m                                                    (3分)       在地面附近有       mg=G                                                   She tried to finish all the work in one day but finally _____ and had to take a rest. A. broke away                   B. broke up                      C. broke down           D. broke out