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InterviewSolution
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In a ballistics demonstration, a police officer fires a bullet mass `50.0g` with speed `200ms^(-1)` on soft plywood of thickness 2.00cm. The bullet emerges only with `10%` of its initial kinetic energy. What is the emergent speed of the bullet ? |
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Answer» Here, `m=50.0g` `=(50)/(1000)kg=(1)/(20)kg` `v_(i)=200ms^(-1)` `:.` Initial K.E., `K_(i)=(1)/(2)mv_(i)^(2)` `=(1)/(2)xx(1)/(20)(200)^(2)=1000J` Final K.E., `K_(f)=10% (K_(i))` `=(10)/(100)xx1000J=100J` If `v_(f)` is emergent speed of the bullet, then `(1)/(2)mv_(f)^(2)=K_(f)` `v_(f)=sqrt((2K_(f))/(m))=sqrt((2xx100)/(1//20))=63.2m//s` Note that K.E. is reduced by `90%` but speed is reduced by nearly `68%`. |
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