题目

The train _____ because of an accident; many passengers are now waiting anxiously at the railway station. A . has been delayed B . delayed C . has delayed D . had been delayed 答案：A光滑平面上一运动质点以速度v通过原点O，v与x轴正方向成α角（如图所示），与此同时对质点加上沿x轴正方向的恒力Fx和沿y轴正方向的恒力Fy，则（　　）A．因为有Fx，质点一定做曲线运动B．如果Fy＞Fx，质点向y轴一侧做曲线运动C．质点不可能做直线运动D．如果Fx＞Fycotα，质点向x轴一侧做曲线运动