[填空题]
A coffee cup on the dashboard of ckt:e id046soa btiif );r,md4t) q.sicar slides forward on the dash when the driver4dsi rm.t t)b,)i;iqf decelerates from 45 $\mathrm{~km} / \mathrm{h}$ to rest in 3.5 s or less, but not if he decelerates in a longer time. What is the coefficient of static friction between the cup and the dash?
