state the law of
conversation of momentum
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Answer:
The law of momentum conservation can be stated as follows. For a collision occurring between object 1 and object 2 in an isolated system, the total momentum of the two objects before the collision is equal to the total momentum of the two objects after the collision.
The magnitude of total final momentum = the magnitude of total initial momentum.
Thus, if no external force is acting on two objects, then their total initial momentum is equal to their total final momentum. This statement is true for any number of objects.
‘When no external force acts on two interacting objects, their total momentum remains constant. It does not change.’
This is a corollary to Newton’s third law of motion. The momentum is unchanged after the collision. The momentum gets redistributed between the colliding objects. The momentum of one of the objects decreases while that of the other increases. Thus, we can also state this corollary as follows.
‘When two objects collide, the total momentum before collision is equal to the total momentum after collision.’
In order to understand this principle, let us consider the example of a bullet fired from a gun. When a bullet of mass m1 is fired from a gun of mass m2, its velocity becomes v1, and its momentum becomes m1 v1. Before firing the bullet, both the gun and the bullet are at rest and hence the total initial momentum is zero. According to the above law, the total final momentum also has to be zero. Thus, the forward moving bullet causes the gun to move backward after firing. This backward motion of the gun is called its recoil. The velocity of recoil, v2 , is such that, m1v1+ m2v2= 0 or v2= -m1/ m2 × v2.