A bullet of mass 50 g moving with an initial velocity of 100 m s-1, strikes a wooden block and comes to rest after penetrating a distance 2 cm in it. Calculate (i) initial momentum of the bullet (ii) final momentum of the bullet, (iii) retardation caused by the wooden block, and (iv) resistive force exerted by the wooden block

Mass (m) = 50 g or 0.05 kg

Initial velocity (u) = 100 m s^-1

Displacement (S) = 2 cm

(i) Initial momentum of the bullet = mass (m) × initial velocity (u)

Substituting the values in the formula above we get,

Initial momentum = 0.05 × 100 = 5 kg m s^-1

Hence, Initial momentum = 5 kg m s^-1

(ii) Final momentum = mass (m) × final velocity (u)

Substituting the values in the formula above we get,

Final momentum = 0.05 × 0 = 0 kg m s^-1

Hence, Final momentum = Zero

(iii) As we know,

v² – u² = 2as

⇒ 0² – 100² = 2 × a × 0.02

⇒ -10000 = 0.04 a

⇒ a = – 10000/0.04 = – 250000 m s^-2

Hence,

Retardation caused by wooden block = 2.5 × 10⁵ m s^-2

(iv) Now, Force (f) = mass (m) × acceleration (a)

F = 0.05 × 2.5 × 10⁵ = 0.125 × 10⁵ N

Hence, The resistive force exerted by the wooden block = 12500 N