Question

A bullet of mass 50 g moving with an initial velocity 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.

Answer 1

Mass, m = 50 gm = 0.05 kg.

Initial velocity, u = 100 m/s.

Final velocity, v = 0.

Distance, s = 2cm = 0.02 m.

(i) Initial momentum = mu = (0.05) (100) = 5 kg m/s^-1

(ii) Final momentum = mv = (0.05) (0) = 0 kg m/s.

(iii) Acceleration, a = (v² - u²)/2s.

Or, a = (0² - 100²)/ 2(0.02). 

Or, a = -2.5  10⁵ ms^-2.

Therefore, retardation is 2.5 × 10⁵ ms^-2.

(iv) Force, F = ma

Or, F = (0.05 kg) (2.5 × 10⁵ ms^-2)

Or, F = 12500 N