Ok.
Im doing higher/A level(I think is the equivalent) physics. Which equations should I use for this ?

"A trolley of mass 2 KG is moving from left to right with a constant velocity of 8m/s when a 1kg mass is dropped vertically onto the moving trolley, sticking to it.
Calculate the resultant velocity of the trolley."

What do I do. Resolution of forces ? Vector diagram ? Is it related to kinetic energy or something ?

Jeez...
this is a stupid thread.