问个sub题，

mike1151UID: 175650

A uniform stick of length L and mass M lies on a frictionless surface. A point particle of mass m approaches the stick with speed v an a straight line perpendicular to the stick that intersects the stick at one end, as shown above. After the collision, which is elastic, the particle is at rest. the speed V of the center of the mass of the stick after the collision is:
a, mv/M
b, mv/(m+M)

图片实在不知道怎么加进来，基本就是一个棍，沿一段有个小球以v速度垂直撞击，小球停止，问棍的质心速度多少，答案选b好像觉得不对阿

wuliUID: 2133814

不说了吗是弹性碰撞。水平动量守恒，又没有固定点，不能用角动量守恒考虑

mike1151UID: 175650

没人说角动量啊，水平动量守恒，答案应该是a啊，小球是弹性碰撞那么就没有粘在杆上，那当然不能是b啊，麻烦兄台仔细看一下我的问题啊？？

wuliUID: 2133814

SORRY,是我看错选项了，同意a