Question

A bullet of mass 200mg moving with a velocity of 100 metre per second penetrates into a number of wooden planks each of thickness 2 cm and offering constant retardation bullet comes to rest when it just enters the 25th plank. The magnitude of resistive force offered by plank is about​

Answer 1

Answer:

If bullet of mass 5 gm moving with velocity 100 m/sec , penetrates the wooden block upto 6 cm . Then the average force imposed by the bullet on the block i

Answer 2

Given:

As per the given data,

• Mass of the bullet (m) = 200 mg =  0.0002 kg
• Initial velocity (u) = 100 m/s
• Thickmess of each plank = 2 cm
• Total no of planks = 25
• Final velocity(v) = 0 m/s [rest]

To find:

• Resistive force offered by the plank.

Method:

Total distance covered by the bullet

= No of planks x thickness of each plank

= 25 x 0.02 m

= 1 m

By using the third equation of motion,

$\implies\sf{v^2 = u^2 + 2as}$

As, v = 0

$\implies\sf{u^2 = - 2as}$

$\implies\sf{a = - 10000/2 \times 1 }$

$\implies\sf{a = - 5000 m/s^2 }$

Note: Here negative sign denotes retardation

____________________

Now,

By applying Newton's second law of motion,

$\implies\sf{F = ma }$

Now let's substitute the values,

$\implies\sf{F = 0.0002 \times - 5000 }$

$\implies\sf{F = - 1 N }$

Hence,

The magnitude of the resistive force offered by the plank is1 N.