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*Question:* Two objects slide over a frictionless
horizontal surface. The first object, mass
, is propelled with
speed
toward the second object, mass
, which is initially at rest. After the collision, both
objects have velocities which are directed
on either side of the
original line of motion of the first object. What are the
final speeds of the two objects? Is the collision elastic or inelastic?

*Answer:* Let us adopt the coordinate system shown in the diagram. Conservation
of momentum along the -axis yields

Likewise, conservation of momentum along the -axis yields

The above pair of equations can be combined to give

and

The initial kinetic energy of the system is

The final kinetic energy of the system is

Since , the collision is *elastic*.

** Next:** Circular motion
** Up:** Conservation of momentum
** Previous:** Worked example 6.5: Elastic
Richard Fitzpatrick
2006-02-02