a bullet travelling horizontally at a speed of 350 m/s hits a board perpendicular to the surface, passes through it and emerges on the other side at a speed of 210 m/s . if the board is 4.00 cm thick, how long does the bullet takes to pass through it ?

Answer 1

In the case of uniform acceleration,
distance = average speed * time
distance = 0.04m
average velocity = (350+210)/2 m/s
= 280 m/s
Time = distance / average speed
= 0.04/280 s
= 1.43*10^-.4 s

Answer 2

Vavg = (210+350)/2 = 280 m/s.

t = d/V = 0.04/280 = 0.00014286 s. =
142.86 uS.