A body pulled by a constant force accelerates from 10 cm?
st case: F1=m*a1 where a1=(v1f-v1i)/t1=(3510)*cm/s/(3.5*s)=7.1*cm/s^2 so F1=m*7.1*cm/s^2 while F2=m*a2 where a2=(v2f-v2i)/t2=(1100)*cm/s/(10.5*s)=10.5*cm/s^2 so F2=m*10.5*cm/s^2 The ratio F2/F1=a2/a1=10.5/7.1=1.5 so F2=1.5*F1=1.5*5N=7.5*N so the second force is 7.5 Newtons. The mass is not required, but from F1=m*a1 we get m=F1/a1= 5*N/(7.1*cm/s^2)=5*kg*m/s^2/(7.1*cm/s^2)=70.4*kg