Experimental questions about the law of momentum

In summary, the law of momentum conservation states that the total momentum of a system remains constant before and after a collision. In the case of two carts initially at rest, the momentum before the collision is 0 and after the collision, it is a non-zero value due to the velocity of the carts. This is not considered an elastic collision, as the kinetic energy before the collision is 0. The type of collision can be determined by comparing the kinetic energy before and after the collision, with a difference indicating an inelastic collision. However, the law of momentum conservation always holds regardless of the type of collision.
  • #1
-EquinoX-
564
1
if say I have two carts that is initially at rest, one of the cart has a plunger and the plunger is set so that it's against the other cart. When I release the plunger both carts will travel at a certain velocity.

The law of momentum conservation says that the momentum of the initial system is the same as the momentum of the final system.

As far as my understanding goes, the momentum before the what we can say "collision" is 0 as both carts has an initial velocity of 0, as they start from rest. While on the other hand the momentum after collision (after I release the plunger) is some number, as the velocity is not 0. So how is it possible that law of momentum holds here?

p initial is not equal to p final

I use p to denote momentum here.

Can someone please help me to clear my understanding
 
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  • #2
Remember that momentum is a vector quantity. So if one cart has a momentum of 2 kg m/s to the left and if the other cart has a momentum of 2 kg m/s to the right then the total momentum is 0.
 
  • #3
if you consider at my example here, would you consider this as an elastic or inelastic collision? also how about the kinetic energy before and after the collision?

as far as I understand, before the collision the kinetic energy is 0 as there is no initial velocity
 
  • #4
-EquinoX- said:
if you consider at my example here, would you consider this as an elastic or inelastic collision? also how about the kinetic energy before and after the collision?

as far as I understand, before the collision the kinetic energy is 0 as there is no initial velocity

Yes, that is correct- so this obviously is NOT an "elastic" collision. In order to conserve energy you would have to consider the work done in pressing in the plunger which turns into kinetic energy when it is released.
 
  • #5
okay, so on whatever type of collision it is (elastic or inelastic), the law of momentum conservation always holds.. however the kinetic energy before and after the collision is not always the same.. if the kinetic energy of before and after is the same then its elastic collision if not then it's inelastic. Am I right?
 
  • #6
Right. :smile:
 

Related to Experimental questions about the law of momentum

1. What is the law of momentum?

The law of momentum states that the total momentum of a closed system remains constant unless acted upon by an external force. In simpler terms, it means that objects will continue moving at a constant speed and direction unless something else causes them to change.

2. How is momentum calculated?

Momentum is calculated by multiplying an object's mass by its velocity. The formula for momentum is p = m x v, where p is momentum, m is mass, and v is velocity. Momentum is measured in kg*m/s.

3. What is the difference between momentum and inertia?

Momentum and inertia are related concepts, but they are not the same thing. Inertia refers to an object's resistance to change in motion, while momentum is a measure of an object's motion. In other words, inertia describes an object's tendency to stay at rest or in motion, while momentum describes its actual motion.

4. How does the law of momentum affect collisions?

The law of momentum is especially relevant in collisions between objects. In an isolated system, the total momentum before a collision is equal to the total momentum after the collision. This means that the total momentum of the objects involved in the collision will not change, but it may be redistributed between them.

5. Is the law of momentum always applicable?

The law of momentum is a fundamental principle in physics and is applicable in most situations involving the motion of objects. However, it may not be applicable in extreme situations such as when dealing with subatomic particles or objects moving at speeds close to the speed of light, where other factors such as relativity come into play.

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