A 5 gm bulet initial velocity is 300ms-1

Question

and after penetrating a 5cm plank then the bulet stopped . So how much time is needed to penetrate the plank..?

Answer 1

V^2 = Vo^2 + 2a*d.
0 = 300^2 + 2a*0.05, a = -900,000 m/s^2.

V = Vo + a*t.
0 = 300-900,000t, t = ?.