Download Conservation of Momentum

Conservation of Momentum
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The total momentum of an isolated or closed
system (no external forces) remains constant.
Total Initial momentum = Total Final Momentum
Two Object Conservation of Momentum (For Objects 1 and 2):
Conceptual Example
Two students (m1 = m and m2 = 2m ) are in rolling chairs. Beginning
from rest, they push off away from each other. Student 1 moves to
the right with a positive velocity.
A. What was the initial momentum of the two students?
B. What can we infer about the velocity of student 2 after they push off
of each other?
Example 4: Chemistry Throwback
An atomic nucleus (mass = 222.0 u) is initially moving at 420.0 m/s. This
nucleus emits an alpha particle (mass = 4.000 u) in the same direction as its
velocity. The new atomic nucleus slows to 350.0 m/s. What is the velocity of
the alpha particle?
(Note: u is the symbol for atomic mass unit, which is a measurement derived
from the kilogram. This problem may be evaluated without converting the
mass of the particles).
Conservation of Momentum
Additional Example
Total momentum of all objects before = Total momentum of all objects after
A full grocery cart (mass = 25 kg) moving with a positive
velocity of 10 m/s collides with an empty one (mass = 8 kg)
also moving in a positive direction with a velocity of 3 m/s.
After the collision, the full cart continues to move forward,
but only with a positive velocity of 1.2 m/s. What is the
velocity of the empty cart after the collision?
Collisions!!
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Three different
kinds of collisions
IMPORTANT: In ALL collisions, momentum is conserved.
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Elastic Collisions
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Inelastic Collisions
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Total Inelastic Collisions
Collisions!
Elastic
Inelastic
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Perfect rebound,
no energy loss
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Some energy
loss
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Momentum
conserved
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Momentum
conserved
KE conserved
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KEo = KEf
KE NOT
conserved
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Total
Inelastic
Objects are
stuck together
after collision
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Momentum
conserved
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KE NOT
conserved
Collision Summary
Collision
Elastic Collision
Inelastic Collision
Total Inelastic Collision
Kinetic Energy
Conserved
Momentum Conserved
YES
YES
NO
YES
NO
YES
Example 5 – Elastic Collision
A 4.00 kg block is moving to the right with a velocity of 10.0 m/s and collides
with a stationary second block (mass = 6.00 kg) in an elastic collision. After
the collision, the 6.00 kg block was seen moving to the right with a velocity
of 8.00 m/s. What is the final velocity for the 4.00 kg block?
*Solve using both conservation of momentum as well as conservation of
kinetic energy.