[填空题]
Two crates, of mass s++ ;zbk2let /: hauyf 1gq3y 2b+whjzs.d0 wd:(afnlxws.5o sn40e:-pawa o75 kg and 110 kg , are in contact and at rest on a horizontal surf p00fws ss:oo4e:n -aw(a xd.n5 wad.lace (Fig. 4-54). A 620$-\mathrm{N}$ force is exerted on the 75$-\mathrm{kg}$ crate. If the coefficient of kinetic friction is 0.15 , calculate
(a) the acceleration of the system,
(b) the force that each crate exerts on the other.
(c) Repeat with the crates reversed.
