Question

A bullet of mass 50 g movingwithe an initial velocity 100 m/sec strikes wooden block and comes to rest after penetrating a distances 2 cm init calculate initial momentum of the bullet ii) final momentum of the bullet iii) retardation caused by the wooden block and resistive force exerted by the women block

Answer 1

$\bold{CONCISE\:PHYSICS \:-\:IX}$

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

Answer 2

Explanation:

Mass=50g i.e. 50/1000kg

Initial velocity=100m/s

Final velocity=0

Distance=2cm i.e. 2/100m

1)Initial momentum=m×u

=(50/1000)×100

=5kgm/s

2)Final momentum=m×v

=(50/1000)×0

=0

3)retardation:

v^2=u^2+2as

0^2=100^2+2×a×2/100

0=10000+a/25

0=(250000+a)25

0×25=250000+a

0=250000+a

-a=250000

a=-250000

i.e. 250000m/s^2

4)Force=Mass×Acceleration

=(50/1000)×250000=

=12500N