A $3\mathrm{.}2-kg$ ball is attached to the end of a $0\mathrm{.}80-m$ string to form a pendulum. This pendulum is released from rest with the string horizontal. At the lowest point of its swing, when it is moving horizontally, the ball collides with a $1\mathrm{.}6$kg block initially at rest on a horizontal frictionless surface. The speed of the block just after the collision is $6\mathrm{.}0\frac{m}{s}.$ What is the speed of the ball just after the collision? $($elastic collision$)$