Physics Sub 一题？

PI2002UID: 65567

40. A uniform stick of length L and mass M lies on a frictionless horizontal surface. A point particle of mass m approaches the stick with speed v at 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 mass of the stick after the collision is
A. mv/M
B. mv/(m+M)

答案给的是B ,
我觉得题目说的应该是M的质心动量啊

auteurUID: 139302

个人觉的给的答案是正确的