(1)1m/s (2)15N
(1)由牛顿第二定律:T-f=ma
得:
,
由
(2)由T-f=ma得:T-μ(mg+F)=ma,
又由
代入上式:4N-0.1(20N+F)=2kg×0.25m/s2得:F=15N