(1)(2分)减小压强 增大摩擦
(2)(3分)推土机做功W = Pt = Fs
F=Pt/s=2.0*10^5w*60s/12m=1.0*10^5N
由于推土机匀速运动,则推土机受到的阻力Ff =1.0 x 105N
