[填空题]
Calculate the force exerted on a rocket, given that the propellkfi*vu q9y( l0ing yaxne.nuh ) 9g2 l2 5cbxnw9j3gases are expelled at a rat2 xhn9jxy9u3n5 n.eb acw l2)ge of $1500 \; kg/s$ with a speed of $ 4\times10^{4 } \; m/s$ (at the moment of takeoff). F = $\times 10^7 \; N$
