Question

A bullet of mass 100g moving with 20 m/s strikes a wooden plank and penetrates upto 20cm . Calculate the resistance offered by wooden plank

Answer 1

Given
mass = 100g=0.1kg
Velocity = 20m/s^2
Penetration Distance = 20cm = 0.2m
Now ,
$\frac{1}{2}mv {}^{2} = resistive \: force \: \times penetration \: distance$

or
$\frac{1}{2} \times 0.1 \times (20) {}^{2} = resistive \: force \times 0.2$
or 20= resistive force ×0.2
Hence Resistance offered =100N .
Hope it helps you

Answer 2

Given:

Mass of bullet,m=100 g

Speed of bullet,v=20 m/s

Distance, s=20 cm

To find:

Resistance offered by wooden plank

Solution:

Distance,s=20 cm=20/100 m=0.2 m

1 m=100 cm

m=100 g=100/1000=0.1 kg

1 kg=1000 g

Work done in stopping bullet=Kinetic energy of bullet

$Resistance\;force\times s=\frac{1}{2}mv^2$

$F\times 0.2=\frac{1}{2}(0.1)(20)^2$

$F=\frac{0.1\times (20)^2}{2\times 0.2}$

F=100 N

Hence, the resistance offered by wooden plank=100 N