A bullet of mass 0.01 kg moving at a speed of 100m/s strikes a wooden plank of thickness 0.1m and emerges with a velocity 25m/s.Find the resistance offered by the plank assuming it to be uniform.

Initial velocity, u = 100 m/s

Final velocity, v = 25 m/s

Mass of bullet, m = 0.01 kg

Thickness of slab, s = 0.1 m

Using,

v² = u² + 2as

=> 25² = 100² + 2a(0.1)

=> a = (25² - 100²)/0.2

=> a = -46875 m/s²

The negative sign indicates that the direction of acceleration is against the direction of motion of the bullet.

Or retardation = 46875 m/s²

So, the resistance force is, F = (0.01)(46875) = 468.75 N