Conservation of Momentum

1
Conservation of Momentum
2
CONSERVATION OF LINEAR MOMENTUM   According to
the law of conservation of linear momentum, the
total momentum in a system remains the same if no
external forces act on the system.
Cars on ice
3
EX 1 A 0.105-kg hockey puck moving at 48 m/s
is caught by a 75-kg goalie at rest. With what
velocity does the goalie slide on the ice after
catching the puck?
M1 0.105 kg M2 75 kg V1 48 m/s V2 0 m/s
p before p after
m1V1 m2V2 (m1 m2) Vf
(0.105 kg)(48m/s) (75kg)(0) (0.105kg 75Kg)
Vf
Vf 0.067 m/s
4
ELASTIC AND INELASTIC COLLISIONS   Elastic
Collision A collision in which objects collide
and bounce apart with no energy loss. Inelastic
Collision A collision in which objects collide
and some mechanical energy is transformed into
heat energy.
5
(No Transcript)
6
The animation below portrays the inelastic
collision between a 1000-kg car and a 3000-kg
truck. The before- and after-collision velocities
and momentum are shown in the data tables.
7
The animation below portrays the elastic
collision between a 3000-kg truck and a 1000-kg
car. The before- and after-collision velocities
and momentum are shown in the data tables.
8
Before the collision, the momentum of the truck
is 60 000 Ns and the momentum of the car is 0 Ns
the total system momentum is 60 000 Ns.
After the collision, the momentum of the truck is
30 000 Ns and the momentum of the car is 30 000
Ns the total system momentum is 60 000 Ns.
9
The animation below portrays the inelastic
collision between a very massive diesel and a
less massive flatcar. The diesel has four times
the mass of the freight car. After the collision,
both the diesel and the flatcar move together
with the same velocity.
10
EX 2 A 0.50-kg ball traveling at 6.0 m/s
collides head-on with a 1.00-kg ball moving in
the opposite direction at a velocity of -12.0
m/s. The 0.50-kg ball moves away at -14 m/s after
the collision. Find the velocity of the second
ball.
M1 0.50 kg M2 1.00 kg V1 6.0 m/s V2
-12.0 m/s Vf1 -14 m/s
p before p after
m1V1 m2V2 m1Vf1 m2V2f
(.5kg)(6m/s) (1kg)(-12m/s) (.5kg)(-14m/s)
(1kg)(V2f)
V2f - 2 m/s
11
EX 3 A 3000-kg truck moving rightward with a
speed of 5 km/hr collides head-on with a 1000-kg
car moving leftward with a speed of 10 km/hr. The
two vehicles stick together and move with the
same velocity after the collision. Determine the
post-collision velocity of the car and truck.
M1 3000 kg M2 1000 kg V1 5.0 km/hr V2
-10 km/hr
p before p after
m1V1 m2V2 (m1 m2 )Vf
(3000kg)(5km/hr) (1000kg)(-10km/hr) (3000kg
1000kg) Vf
Vf 1.25 km/hr, right
12
(No Transcript)
13
For the remainder of class...  PSE Chapter 4 pg
58 7-14 due BOC 12/9