Jining Medical Equipment Spring

A. Taking the container and the whole ball as the research object, the force analysis shows that there is total gravity and ground support in the vertical direction, and there is no friction force on the hemispherical container in the horizontal direction. So, A is wrong.

Force analysis of balls B and C: gravity G, elastic force F of spring and supporting force N of container, as shown in the figure. From the balance condition and geometric relationship, we can see that N=F=mg, so B is wrong; C is correct;

D, according to Hooke's law: if the compression of the spring is x=Fk=mgk, the original length of the spring is R+x=R+mgk, so D is correct.

So choose CD.