In some demonstration, a police officer fires a bullet of mass 50.0g with speed `200ms^(-1)` on soft plywood of thickness 2.00 cm. The bullet emerges with only 10% of its initial kinetic energy. What is the emergent speed of the bullet?

Explanation

Initial kinetic energy,
`KE_(i)=(1)/(2)xx(50)/(1000)xx200xx200J`
`=1000J`
Final kinetic energy,
`KE_(f)=(10)/(100)xx1000J=100J`
If `v_(f)` is emergent speed of the bullet, then
`(1)/(2)xx(50)/(1000)xxv_(f)^(2)=100`
or `v_(f)^(2)=4000` (or)
The emergent speed
`v_(f)=63.2ms^(-1)`