Question

15. A bullet of mass 50 g moving with an initial velocity
of 100 m sl, 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
Ans. (1) 5 kg m s', (ii) zero,
(iii) 2.5 x 105 m s?, (iv) 12500 N​

Answer 1

Explanation:

given,

u =100m/s ; m=50g = 0.05kg ; s=2cm = 0.02m

v=0 ( as it come to rest)

1) initial momentum = mu = 0.05kg × 100m/s

=> initial momentum = 5kgm/s

2) final momentum = mv = 0.05kg × 0

=> final momentum= 0

3) using v²-u²=2as

=> (0)² - (100)² = 2(a)(0.02)

=> 2(0.02) a = (-) 10000

=> a = (-) 250000 m/s² = (-) 2.5×10⁵m/s²

but here , retardation is asked

retardation = (-) a

=> retardation = 2.5×10⁵m/s²

4) resistive force = m×retarding acceleration

=> F = 0.05 × 2.5×10⁵

=> F=12500N