[填空题]
Calculate the force exerted on a lbp8g;( z3sr li5arg *rocket, give od hvk6-,n)c1 md9xddn that the propelling gases are expelled at a rate odd1 v9h o6mk,n )dx-cdf 1500kg/s with a speed of $ 4\times10^{4 }$ (at the moment of takeoff).$a\times10^7$ N a =
