acceleration of rocket is given here as
[tex]a_y = 2.60* t[/tex]
now we know that
[tex]\frac{dv}{dt} = 2.60t[/tex]
now integrating both sides
[tex]\int dv = \int 2.60t dt[/tex]
[tex]v = 2.60\frac{t^2}{2}[/tex]
[tex]v = 1.30 t^2[/tex]
here since its given that rocket will accelerate for t = 10 s
so here we have
[tex]v = 1.30 * 10^2[/tex]
[tex]v = 130 m/s[/tex]
so after t = 10 s the speed of rocket will be 130 m/s upwards