Answer
19 m/s
Explanation
Finding the velocity of the initial object
Momentum=mass × velocity
P=m×v
4000=115 × v
v=4000/115 =34.78⇒35m/s
Total momentum after the collision
Because the momentum is conserved, the total momentum afterwards =4000kg-m/s
Total mass after collision
Total mass = mass of initial object + mass of second object
Total mass= 115+100= 215kg
Finding new velocity after collision
v=p/m
=4000/215
=18.60
=19m/s