Question

高一物理题目http://wenku.baidu.com/link?url=HF6ssSbjVZOxdIi96Lrysy

Answer 1

mgh=1/2(M+m)v2^2-1/2(M+m)V1^2

0.55=0.5(M+m)(3-0.25)

M+m=0.4kg

M=0.3kg