20. A 2.0-kg block is released from rest at the top of a 22° frictionless inclined plane of height 0.65 m (Fig. 6-35).
At the bottom of the plane it collides with and sticks to a block of mass 3.5 kg. The two blocks together slide a distance of 0.57 m
across a horizontal plane before coming to rest.
What is the coefficient of friction of the horizontal surface?