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Momentum: A measure of the motion of a body equal to the product of its mass and velocity. Also called linear momentum. Symbolized universally by the letter P.
All bodies in motion have a certain amount of momentum but dependent on the amount of velocity and mass the given body has the amount of momentum will vary. Being that momentum is a vector quantity, or a quantity that is defined by both direction and magnitude, it is imperative to note both the value of the momentum of the given body but also the direction which the momentum is going.
Since the equation for momentum is: Momentum=Mass x Velocity or P=mV it can be said that if one variable remains constant, the value of the other variable will dictate the resulting Momentum value.
EX: A 5.0KG newborn rolls down fifth avenue at a constand speed of 20 m/s, What is its resulting momentum?
Determining the magnitude of this problem is quite simple. Using the equation for momentum:P=MV, and using simple substitution, we get the following, P=(5.0KG) x (20 M/S) resulting in p= 100 KGM/S.
Determining the direction in this problem is fairly simple as well, as most New Yorkers should know, Fifth Avenue runs from North to South, so if the baby rolled down Fifth Avenue s/he would be rolling South.
Momentum In a Closed System:
Closed System: A system that doesn't gain or lose mass.
Internal force: All the forces within a closed system.
Law of Conservation of Momentum:Weather the objects stick together or come apart in a collision, the momentum of a closed system with no net external force does not change.
The equation that demonstrates these definitions is: PA1+PB1=PA2+PB2 in order to solve for mass and velocity this equation can be broken down to: mAvA1 + mBvB1= mAvA2 + mBvB1
Here is a sample problem: A 2275kg car going 28m/s rearends an 875kg compact car going 16m/s on ice in the same direction. The two cars stick together. How fast does the wreckage move immediately after the collision?
Answer:
 v2=(2275kg)(28m/s)+(875kg)(16m/s) /(2275kg+875kg)
 v2=25m/s