A bullet traveling horizontally at a speed of 350\ \mathrm{m/ s}350 m/s hits a board perpendicular to its surface, passes through and emerges on the other side at a speed of 210\ \mathrm{m/ s}210 m/s. If the board is 4.00\ \mathrm{cm}4.00 cm thick, how long does the bullet take to pass through it?
