[问答题]
A block of mass M is u .co-5 i1qevlsuspended from a ceiling by a spr kzuzcu:;o b.3ing with spring stiffness constant k. A penny of mass m is placed on top of the block. What is the maximum amplitude of oscillations that will allow the penny to just stay on top of the block? (Auc3obz.k;u : zssume $m \ll M$)