Correct Answer - C
`(f_(s))_(max) = 30 N,f_(x) = 20 N` block will start moving at `t=3 sec` after `3 sec` by `F_("net") = ma`
`rArr 10 t - 20 = 10 a rArr a =t -2`
`underset(0)overset(v)(int) dv = underset(3)overset(5)(int) (t-3)dt=v=4 m//s`
`rArr K.E = (1)/(2) xx 10 xx 4_(2) = 80 J`