Download Law of Conservation of Momentum

Law of Conservation of Momentum
 In the absence of external impulses, the total
momentum of a system remains constant.


pTOTAL (i )  pTOTAL ( f )
Momentum can be transferred from one
part of a system to another, but the total
amount remains constant.
 Momentum is conserved during any interaction among
objects – collisions, explosions, etc. – since these
interactions involve INTERNAL impulses (one part of
the system exerting a force on another part).
Application #1:
A car of mass 1000. kg traveling east at 25.0 m/s
collides with a stationary truck of mass 3000. kg.
If the vehicles slide off together after the collision,
what is their velocity?
0 m/s
25.0 m/s
BAM!

v


pTOTAL (i)  pTOTAL (f)
Two separate parts to the system before the collision,
and only one part after the collision.



pcar (i)  ptruck (i)  p(f)



mvcar (i)  mvtruck (i)  mv(f)

(1000. kg) ( 25.0 s )  0  (1000. kg  3000. kg) v(f)


kgm
25,000 s  (4000. kg) v(f)

m

6.25
m
s
 
 v(f)  6.25 m s , east
Application #2:
A motionless grenade explodes into two pieces. A
1.0-kg piece flies north at 100. m/s. What is the
velocity of the other piece if its mass is 3.0 kg?
100. m/s

v