Question

In a ballistic demonstration, a police officer fires a bullet of mass `50g` with a speed of `220m//s` on a wooden target. The bullet emerges with `20%` of its initial `K.E.` What is the emergent speed of the bullet ?

Answer 1

Here,`m=50g=(50)/(1000)kg=(1)/(20)kg`
`u=220m//s`
Initial KE of bullet, `E_(1)=(1)/(2)m u^(2)`
`E_(1)=(1)/(2)xx(1)/(20)xx(220)^(2)=1.21xx10^(3)J`
Final KE of bullet, `E_(2)=20%E_(1)`
`=(20)/(100)xx1.21xx10^(3)J=0.242xx10^(3)J`
From `E_(2)=(1)/(2)m upsilon^(2)`
`upsilon=sqrt((2E_(2))/(m))=sqrt((2xx0.242xx10^(3))/(1//20))`
`upsilon=98.38m//s`