Conservation of Momentum

1
Conservation of Momentum
The Law of

• Momentum before interaction Momentum after
  interaction

2
Momentum Rocket Momentum Exhaust A huge 20-kg
rocket zooms upward at 5 meter/second. At the
same exact time, 10-kg of water shoots downward.
How fast does the water shoot out?
3
Momentum Rocket Momentum Exhaust mv mv 20 x 5
10 x ??? 100 10 x ???
4
Momentum Rocket Momentum Exhaust mv mv 20 x 5
10 x ??? 100 10 x 10 m/s
5
A toy 10-kg fire truck is rolling at 10 m/s when
it hits a parked 5-kg toy car
mv 10 x 10
mv 5 x 0
6
After the collision, the car rolls at 4 m/s. What
is the velocity of the fire truck?
mv 5 x 4
mv 10 x ?
7
mv mv mv 10 x 10 10v (5 x 4) 100 10v
20 -20 -20 80 10v 10 10 v
8 m/s
8
A blue 10- kg box car rolls at 6 m/s and crashes
into a 20-kg box car that is at rest.
6 m/s
0 m/s
10 kg
20 kg
9
A blue 10- kg box car rolls at 6 m/s and crashes
into a 20-kg box car that is at rest.
6 m/s
0 m/s
10 kg
20 kg
After the crash, both cars are stuck together.
What is their velocity?
? m/s
10 kg
20 kg
10
After the crash, both cars are stuck together.
What is their velocity?
? m/s
10 kg
20 kg
mv mv mv (10x6) (20x0) 30V 60 30V V 2
m/s
11
Law of Independence of MotionGravity doesnt
care if an object is moving horizontally or
vertically, it will still cause it to fall at 9.8
m/s2.For example, if I threw a rock off of a
cliff and my friend just dropped another rock at
the same time, both rocks would hit the water at
the same time (one would just land farther away
from the cliff).