题目

如图所示，某物体沿光滑圆弧轨道由最高点滑到最低点的过程中，物体的速率逐渐增大，则( )A. 物体的合力为零B. 物体的合力大小不变，方向始终指向圆心OC. 物体的合力就是向心力D. 物体的合力方向始终与其运动方向不垂直(最低点除外) 答案：【答案】D【解析】物体做加速曲线运动，合力不为零，A错误；物体做速度大小变化的圆周运动，合力不指向圆心，合力沿半径方向的分力等于向心力，合力沿切线方向的分力使物体速度变大，即除在最低点外，物体的速度方向与合外力的方向夹角为锐角，合力与速度不垂直，B、C错误，D正确。 短文理解。根据你听到的短文内容和五个问题。从A、B、C中选出与你听到的短文内容相符的答案。短文读2遍。 (     )1.A. Three.                                     (     )2.A. In a library.                          (     )3.A. She wanted to stay                at home and watch TV.   (     )4.A. Her parents.                             (     )5.A. It was exciting                but very scary.          B. Four.                              B. At a restaurant.                 B. She wanted to work     in a restaurant. B. Her friend.                        B. It was boring     but funny.           C. Two.                                 C. At home.                            C. She want to study     until 12:00 pm.   C. Her brother.                           C. It was old but      interesting.