[填空题]
Estimate (a) how long it tookp .m ky4oe98jj c7u9w73zizlx a stone to fall st+/,ylow3w9 5kefgr8la mvl i0raight down from the top of the Empire State Building (420 m hig 8m+wvl, /53walo0k r9lfgy eih) $s$, and (b) its velocity just before landing? $m/s$