In a ballistics demonstration a , police officer fires a bullet of mass 50 g with speed `200ms^(-1)` on soft plwood of thickness 2 cm . The bullet emerges with only 10 % of its initital kinetic energy . What is the emergent speed of the bullet ?

Explanation

Mass of bullet m = 50 g = 0.05 kg
Initial velocity `V_(@)=200m//s`
Initial K.E `(1)/(2)mv_(0)^(2)=(1)/(2)xx(50)/(1000)xx200xx200=1000J`
Final K.E . 10 % of 1000 J = 100 J
But K.E = `(1)/(2)mv_(f)^(2)rArrv_(f)=sqrt((2KE)/(m))`
`v_(f)=sqrt((2xx100)/(0.05))=sqrt(4000)=20sqrt(10)=63.2m//s`