A bullet initially moving with a velocity of 20 m/s strikesa target and comes to rest after penetrating a distance 10cm in the target . Calculate the retardation caused by the target .

Initial velocity, u = 20 m/s

Final velocity, v = 0

Distance travelled, s = 10 cm = 0.1 m

Now, using,

v² = u² + 2as

=> 0 = 20² + (2)(a)(0.1)

=> a = -2000 m/s²

This is the acceleration of the bullet. So, the retardation is = 2000 m/s²