I am very sorry I don’t know
Answer:
The momentum would be doubled
Explanation:
The magnitude of the momentum of the freight train is given by:

where
m is the mass of the train
v is its speed
In this problem, we have that the speed of the train is unchanged, while the mass of the train is doubled:

therefore, the new momentum is

so, the momentum has also doubled.
The acceleration formula goes like this: a= (vf-vi)/t so it would be (13-4)/3 Thus the answer is 3m/s^2
This theory was first proposed by Nicolaus Copernicus. Copernicus was a Polish astronomer. He first published the heliocentric system in his book: De revolutionibus <span>orbium </span>coelestium<span> , "On the revolutions of the heavenly bodies," which appeared in 1543.</span>