Answer:
v₂ = -3.42 m/s
Step-by-step explanation:
Given that,
Mass of an object, m₁ = 3.6 kg
Initial speed of this object is, u₁ = +6.5 m/s (positive for right)
Mass of another object, m₂ = 5 kg
Initial velocity of this object, u₂ = -4 m/s (negative for left)
Fina velocity of object 1, v₁ = 5.7 m/s
We need to find the final velocity of object 2 i.e. 5 kg object.
It is a concept based on the conservation of momentum. Using the conservation of momentum as follows :

v₂ is the final velocity of 5 kg object.
Putting all the values to find it.

So, the final velocity of the object 2 is 3.42 m/s and it is towards left.