Download Hint

Unit 7.2 Conservation of
Momentum
Teacher: Dr. Van Der Sluys
Objectives
• Collisions
• Law of Conservation of Momentum
• Simple Collision Problems
– Elastic
– Inelastic
Momentum
For an individual object
p = mV
For a system involving multiple objects
 p =  mn v n
Where mnvn are the momentums of each of the
individual objects in the system.
Collisions
• Elastic collisions between objects result
in rebounds, so that the total kinetic
energy of the system remains the same.
• Inelastic collisions result when the
objects in the system stick together and
there is a conversion of some kinetic
energy into other forms of energy.
Law of Conservation of
Momentum
• For any two body system the total
momentum before and after a collision
must be equal.
m1v1 + m2v2 = m1v1’ + m2v2’
• The law of Conservation of momentum
states that the total momentum of an
isolated system is always constant.
Conservation of Momentum Rifle recoil
What is the recoil velocity of a 6.0 kg shot
gun that shoots a 0.150 kg deer slug at a
speed of 120 m/s?
Hint: Draw a vector diagram representing
both the velocity and momentum of both
the bullet and the gun before and after the
bullet is fired.
Conservation of Momentum Simple Inelastic Example
An empty 10,000 kg railroad car traveling
at a speed of 24.0 m/s strikes an identical
railroad car that is stationary. If the
couplings cause the cars to lock together
as a result of the collision, what is their
velocity after the collision?
Conservation of Momentum Simple Inelastic Example
An empty 10,000 kg railroad car traveling
at a speed of 24.0 m/s strikes loaded
railroad car having a mass of 20,000 kg
that is stationary. If the couplings cause
the cars to lock together as a result of the
collision, what is their velocity after the
collision?
Conservation of Momentum Simple Inelastic Example
An empty 10,000 kg railroad car traveling
at a speed of 24.0 m/s strikes loaded
railroad car having a mass of 20,000 kg
that is moving with a velocity of -12.0 m/s.
If the couplings cause the cars to lock
together as a result of the collision, what
is their velocity after the collision?
Simple Systems Involving
Elastic Collisions
• http://www.hazelwood.k12.mo.us/~grichert/ex
plore/dswmedia/airtrack.htm
• Try some of the following and predict what
will happen after the elastic collision.
– m1 = m2, v1 = 5.0 m/s and v2 = 0 m/s (Can you
predict? How do you know?)
– m1 = 1.0 kg and m2 = 2.0 kg, v1 = 5.0 m/s and v2 =
0 m/s
– m1 = m2, v1 = 5.0 m/s and v2 = -5.0 m/s
– Try others of your choice (Can you predict? If not,
why not?)
A Really Complicated System
Involving Elastic Collisions in Two
Dimensions
http://en.wikipedia.org/wiki/Elastic_collision