Perfectly Inelastic Ball Collision: Final Velocities of Both Balls

[PnotConserved]

Ball 1, with a mass of 100 g and traveling at 10 m/s, collides head-on with Ball 2, which has a mass of 300 g and is initially at rest. What are the final velocities of each ball if the collision is perfectly inelastic?


We're suppose to be talking about Energy, but I figured I could use:

mv+mv (initial)=mv (final)



I got 2.5 m/s for both balls, because if the objects are inelastic they will be traveling at the same speed after collision and momentum is conserved.
Is this right?

 

[LowlyPion]

That would be correct.

 

[PnotConserved]

but now I just tried to use conservation of Energy and got a different answer. I tried
1/2 mv^2 + 1/2 mv^2 = 1/2mv^2 (final for system)

I got both balls traveling at 5 m/s ??

 

[LowlyPion]

but now I just tried to use conservation of Energy and got a different answer. I tried
1/2 mv^2 + 1/2 mv^2 = 1/2mv^2 (final for system)

I got both balls traveling at 5 m/s ??

Kinetic energy is not conserved in an inelastic collision.

 

[PnotConserved]

I tried the V' substitution before but was wrong.

The expression that the book describes it to be:
---> the square root of [(m+M)kd^2] / m^2

 

[The Liberator]

You might want to find out the kinetic energy of the balls before the collision, because you are talking about a change in energy.