I was able to get the answer to Conservation of Momentum but couln't get the same answer using conservation of energy? Steps are shown below. Where did i go wrong using the conserv. of engery method? Assume frictionless surface and inelastic collision.(adsbygoogle = window.adsbygoogle || []).push({});

Q: A 10 gram bullet with a velocity of 1000 m/sec strikes a 100 gram block of wood initially at rest. What is their combined velocity? Can you work the problem using the principle of Conservation of Momentum? Conservation of Energy?

using Momentum:

m1v1+m2v2= (m1+m2)vf, v2=0, m1=mass of bullet, m2=mass of block

v1=velocity of bullet, v2=velocity of block

vf=combined velocity

so vf= (m1v1)/(m1+m2) = (10*1000)/(110)~91 m/s

Using Cons. of Energy:

KE1 + PE1 = KE2 + PE2, KE=kinetic energy, PE=potential E

(1/2)m1(v1)^2 = (1/2)(m1+v2)vf PE1=PE2=0

-if solved for vf, the aswer would be different from the momentum method

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# Homework Help: Conserv. of Momentum and Energy Question

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