An aricraft carrier has a mass of 8.6*10^7 kg and can cruise at 80 km/h.

a) What is the work required to stop it?

B) If only half of the work required to stop it is done, what is its final speed in km/h

For a) I found 2.123*10^10 which is the right answer but I cant find b i don't understand

80 km/h = 80000/3600 =22.22 m/sþ

W=ΔKE= mv²/2=
8.6•10⁷•(22.22) ²/2=2.123•10¹⁰ J
W₁=W/2 =1.062•10¹⁰ J
W₁=ΔKE₁=mv₁²/2
v₁=sqrt(2W₁/m) = 15.71 m/s