Answer:
The velocity would decrease
Step-by-step explanation:
Let
= Mass of car
= Mass of trash can
= Initial velocity of car = 10 m/s
= Initial velocity of trash can = 0
v = Velocity of combined mass
From the question the momentum balance of the system will be

The velocity would decrease as now the mass of the car and trash will both be moving as one. The mass would increase resulting in a lower velocity of the combined mass.