[填空题]
Piles of snow on slippery zfabfy : ;w qw095czf +/+wstrroofs can becomero0*gm j(1hlhc /ztez d*v5* c dangerous projectiles as they melt. Considzh1j0tz o*vl g*mcd*5 rc/(heer a chunk of snow at the ridge of a roof with a pitch of $ 30^{\circ}$ .
(a) What is the minimum value of the coefficient of static friction that will keep the snow from sliding down?
(b) As the snow begins to melt, the coefficient of static friction decreases and the snow eventually slips. Assuming that the distance from the chunk to the edge of the roof is 5.0 m and the coefficient of kinetic friction is 0.20 , calculate the speed of the snow chunk when it slides off the roof.
(c) If the edge of the roof is 10.0 m above ground, what is the speed of the snow when it hits the ground?
