- #1

yungman

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I have a question about momentum vs kinetic energy.

For example, a block C with velocity Vc and mass=2m hit a block B with mass=m at stand still on a LEVELED frictionless track( no change of potential energy). The two block stick together and move at velocity Vcb. Find the relation of Vc vs Vbc.

If I use m1V1 = m2v2, then 2mVc=3mVbc, so final velocity Vbc = 2/3Vc.

But if I use 1/2 (2m)Vc^2= 1/2 (3m) Vbc^2, then Vbc= sqrt( 2/3) Vc.

Why is the two answer different using momentum and kinetic energy equation?

Thanks

For example, a block C with velocity Vc and mass=2m hit a block B with mass=m at stand still on a LEVELED frictionless track( no change of potential energy). The two block stick together and move at velocity Vcb. Find the relation of Vc vs Vbc.

If I use m1V1 = m2v2, then 2mVc=3mVbc, so final velocity Vbc = 2/3Vc.

But if I use 1/2 (2m)Vc^2= 1/2 (3m) Vbc^2, then Vbc= sqrt( 2/3) Vc.

Why is the two answer different using momentum and kinetic energy equation?

Thanks

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