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A bullet after entering a wooden block at rest covers 30 cm inside it and loses half of its velocity. After how much further distance will it come to rest?

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Try an exponential model: dV/dx=-k*V

V=V0*exp(-k*x) and use the data given: v=v0/2 if x=30 to find k

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This is incorrect--- you should assume that the work done per unit distance is constant, since you are breaking the same kind of bonds. 3/4 of the energy is dissipated already, and it needs to dissipate the remaining 1/4, so it will travel 1/3 the distance further, or 10 cm more. The exponential model of slowdown in time is wrong, it's a square-root model in distance. – Ron Maimon Jul 27 '12 at 5:57

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