**This is a SPECIAL RELATIVITY QUESTION**

Say two balls of putty, moving relativistically, collide (although i understand this is not possible theoretically and realistically). They collide at a slight perpendicular displacement, instead of head-on, so that in the final state the stuck together system is rotating. Compared to the non-rotating head-on collision, how will this effect the final speed, and how will this effect the Mf' (final mass)? Imagine that you stop the lump from spinning, will its mass be great. less, or equal to Mf'?

Thank you so much!