Question

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​

Answer 1

Answer:Make sure all concepts are cleared, even regarding how to solve any numericals. Then you can proceed as under.

First of all, write all the given details with appropriate symbols (if any).

✔ Mass (m) = 50 g = 0.05 kg

✔ Initial velocity (u) = 100 m/s

✔ Final velocity (v) = 0 m/s

✔ Distance penetrated (s) = 0.02 m

[i] Bullet's Initial momentum :

mu = 0.05 × 100 = 5 kg.m/s

[ii] Bullet's Final momentum :

mv = 0.05 × 0 = 0 kg.m/s

[iii] Retardation caused by the wooden block :

We know, v² - u² = 2as

Or, (0)² - (100)² = 2×a×0.02

Or, - 10000 = 0.04a

Or, a = - 250,000

Here, negative sign (-) actually indicates negative acceleration or retardation which actually says that there is a decrease in velocity for which it undergoes retardation.

Numerically, we can say, retardation caused by the wooden block is 2.5×10^5 m/s²

[iv] Resistive force (F) = ma

Or, F = (0.05 × 2.5 × 10^5) N

Or, F = 12500 N

:)