The model is based on hypothesis to get an initial idea for analyzing a complex problem. Hence, the validity of a model is limited and may not be valid universally. On the other hand, theories and laws are confirmed hypothesis which are universally valid. These are formulated after repeated testings. theories are more explanatory.
The key to solve this problem is the conservation of momentum. The momentum of an object is defined as the product between the mass and the velocity, and it's usually labelled with the letter
:

The total momentum is the sum of the momentums. The initial situation is the following:

(it's not written explicitly, but I assume that the 5-kg object is still at the beginning).
So, at the beginning, the total momentum is

At the end, we have

(the mass obviously don't change, the new velocity of the 15-kg object is 1, and the velocity of the 5-kg object is unkown)
After the impact, the total momentum is

Since the momentum is preserved, the initial and final momentum must be the same. Set an equation between the initial and final momentum and solve it for
, and you'll have the final velocity of the 5-kg object.
In Newton's Third law of motion, the 'action' and 'reaction' forces act on different objects. That's why they don't cancel each other out and always result in zero force.
Answer:
<h2>3,2 oky na dekh Lena ek bar</h2><h2>2,5</h2>
Acceleration is the change in velocity