A Piece of Taffy Slams into and Sticks to an Identical

Multiple Choice

A piece of taffy slams into and sticks to an identical piece of taffy at rest. The momentum of the combined pieces after the collision is the same as before the collision, but this is not true of the kinetic energy, which partly degrades into heat. What percentage of the kinetic energy becomes heat?

A) 0%
B) 25%
C) 50%
D) 75%
E) need more information