Rotational Motion

A girl of mass M stands on the rim of a
frictionless merry-go-round of radius R and
rotational inertia I, that is not moving. She
throws a rock of mass m horizontally in a
direction that is tangent to the outer edge of
the merry-go-round. The speed of the rock,
relative to the ground is v. Afterwards, the
linear speed of the girl is