Impulse is equal to change in momentum. So if impulse is 2000 then to solve for new velocity we just set it equal to equation for momentum.
First find original momentum by p=mv p=1000*20=20000
So then taking that value minus the impulse since it was in opposite direction of original momentum it will slow it down some. To find new velocity we just take
20000-2000=18000=mv
v=18000/1000 =18m/s
Hope this helps!! Any questions please ask!! Thank you!