Question

In a ballistic demonstration, a police officer fires a bullet of mass 50g with a speed of 200m/s on soft plywood of thickness 2cm. The bullet emerges with only 10% of its initial K.E. What is the emergent speed of the bullet?

Answer 1

Mass of bullet = m = 50g = 0.05kg 

Initial velocity of bullet = u = 200 m/s 

Initial energy of the bullet, ½ mu square  = ½ (0.05)(200 square)  = 1000J 

The bullet emerges with only 10% of its KE. Let the final velocity with which it emerges to be v 

So, final KE is ½ mv square = 10% of ½ mu square  

= ½  mv square = (10/100) x 1000 

= v square = 100 x 2/0.05 

= v = 63.24 m/s

Answer 2

Answer:63.24 m/s

Explanation:

Here initial speed and final speed are given; also the mass of the bullet is given. In this case, initial kinetic energy and final kinetic energy can be calculated from the given data.

Mass = m = 50g = 0.05kg

Initial velocity  = u = 200 m/s

Initial energy = ½ mu square  = ½ (0.05)(200 square)  = 1000J

The bullet emerges with only 10% of its KE.

Let the final velocity with which it emerges to be v

KE is ½ mv square = 10% of ½ mu square  

= ½  mv square = (10/100) x 1000

= v square = 100 x 2/0.05

= v = 63.24 m/s

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