Transcript Momentum Part 2

Momentum Part 2
By: Heather Britton
Conservation of Momentum
• The law of conservation of momentum
states: The total momentum of an isolated
system of bodies remains constant
• By system we mean a set of objects that
interact with each other
• Isolated system means the only forces
present are between the objects of the
system
Conservation of Momentum
• If two people on rollerblades push off of each
other the momentum one person has will
equal the momentum of the other person
• Rockets are propelled by conservation of
momentum
• The “kick” from firing a gun is conservation of
momentum
Conservation of Momentum
• The law of conservation of momentum is
very closely related to Newton’s third law of
motion
• When one object exerts a force on a second
object, the second object exerts an equal
and opposite force on the first
• The time the two objects are in contact is
equal, so the change in momentum is equal
but opposite (ΣFΔt = Δp)
Conservation of Momentum
Object
1
2
System
Initial
momentum
p1o
p20
p1o + p20
Impulse
+FΔt
-FΔt
0
Momentum
change
Final
momentum
+Δp
-Δp
0
p1
p2
p1 + p 2
Conservation of Momentum
• po = p
• p10 + p2o = p1 + p2
• m10v10 + m2ov2o = m1v1 + m2v2
Example 4
• An astronaut at rest in space with a mass of
84 kg fires a thruster that expels 35 g of hot
gas at 875 m/s. What is the velocity of the
astronaut after firing the shot?
Collisions and Conservation
of Momentum and Energy
• In a collision the law of conservation of
momentum holds true
• The total momentum before the collision is
the same as the momentum after the
collision
• The total amount of energy is conserved as
well
• Kinetic energy is not always conserved
Example 5
• Glider A of mass 0.355 kg moves along a
frictionless air track with a velocity of 0.095
m/s. It collides with gilder B of mass 0.710
kg moving in the same direction at a speed
of 0.045 m/s. After the collision glider A
continues in the same direction with a
velocity of 0.035 m/s. What is the velocity of
glider B after the collision?