Momentum of expelled gases = momentum gained by ship.
Momentum of expelled gasses = 1000x1000 = 1,000,000
1,000,000 = momentum gained by ship
1,000,000 = 49 000 x V (50,000kg - 1000kg from expelled gases)
V = 20.41
total velocity = initial velocity + velocity gained
=100+20.41
=120.41