# Perfectly Inelastic

#### 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?
1. Homework Statement

2. Homework Equations

3. The Attempt at a Solution

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#### LowlyPion

Homework Helper
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

Homework Helper
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.

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