Answer:
trial 3, because this trial has a large mass and a large velocity
Step-by-step explanation:
The momentum of each cart at the bottom of the ramp can be calculated as follows:

where
m is the mass of the cart
v is the velocity of the cart at the bottom of the ramp
Let's use this formula to calculate the momentum of each cart:
- cart 1: 

- cart 2: 

- cart 3: 

- cart 4: 

So, we see that cart 3 is the one with largest momentum.