Popular Units And Dimensions Questions

A rocket with a lift-off mass 20,000 kg is blasted upwards with a an initial acceleration of 5 m/s^2 .Calculate:- the initial force of the blast :- 1) 1 x 10^5 N 2) 3 x 10^5 N 3) 2 x 10^5 N 4) 4 x 10^5 N ...

we know g=9.81 and if we calculate we should get π2=9.87.These 2 values are almost same!!!!! Why give reason??????? ...