F=F1-G=70-(5*10)=20N;P=F/S=20/(0.2*0.2)=500Pa
F=F1-mg=70-(5*9.8)=21N;P=F/S=21/(0.2*0.2)=525Pa
F=F1-G=70-(5*10)=20N;P=F/S=20/(0.2*0.2)=500Pa 就这样子啦、