Momentum

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Chapter 9 Momentum Its Conservation
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9.1 Impulse Momentum
Momentum is a vector quantity That is defined as
the product Of an objects mass and velocity.
p mv
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Problem...
A 2250 kg pickup truck has a Velocity of 25 m/s
to the east. What is the momentum of The
truck?
56250 kg m/s
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Problem...
A 21 kg child is riding on a 5.9 kg Bike with a
velocity of 4.5 m/s To the north west. What is
the Total momentum of the child bike Together?
Just the child? Just The bike?
120 kg m/s 94 kg m/s 27 kg m/s
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A change in momentum Takes force and time.
The Impulse-Momentum Theorem
F?t ?p
or
F?t mvf - mvi
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Impulse (for a constant external Force) is the
product of the Force and the time over which It
acts on an object.
F?t is called the Impulse.
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Problem...
A 1400 kg car moving westward With a velocity of
15 m/s Collides with a utility pole. It is
then Brought to a stop in 0.30s. Find The
magnitude of the force Exerted on the car during
the Collision.
7 X 104N
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Stopping times and distances Depend on the
impulse- Momentum theorem.
A change in momentum over A longer time requires
less force.
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Angular momentum is the product Of a rotating
objects moment Of inertia and angular Speed
about the same axis.
L I?
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Problem...
Erica, 65kg, is spinning on a merry- Go-round
that has a mass of 115kg, And a radius of 2m. She
walks From the edge to the center. If The
angular speed is initially 2 rad/s What is its
angular speed when she Reaches a point 0.5m from
The center?
3.9 rad/s
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The angular impulse-momentum Theorem states that
the angular Impulse on an object is equal To the
change in the objects Angular momentum.
t?t Lf - Li
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9.2 Conservation of Momentum
The total momentum of all objects Interacting
with one another Remains constant regardless of
The nature of the forces Between the objects.
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The conservation of momentum Can be shown as a
formula
m1v1i m2v2i m1v1f m2v2f
Momentum is conserved in Collisions and for
objects Pushing away from each other.
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Problem...
A 76 kg boater (Charlie), initially At rest in a
stationary 45 kg boat, Steps out of the boat and
onto the Dock. If Ryan moves out of the Boat
with a velocity of 2.5 m/s, What is the final
velocity Of his boat?
v2f 4.2 m/s
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Problem...
An 85 kg fisherman jumps from a Dock into a 135
kg rowboat at rest On the west side of the dock.
If the Velocity of the fisherman is 4.3 m/s to
the west, what is the Final velocity of the
Fisherman and the boat?
1.66 m/s to the west
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Elastic Inelastic Collisions
There are two kinds of collisions Those that
bounce off of each other And those that stick
together
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A perfectly inelastic collision is a Collision in
which two objects Stick together and move with A
common velocity after Colliding.
The formula for a perfectly Inelastic collision
m1v1i m2v2i (m1 m2) vf
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Problem...
An 1850 kg Cadillac stopped at a Light is struck
from the rear by A Honda with a mass of 975 kg.
The 2 cars become entangled. If the Honda was
moving at 22 m/s to the north before, what Is
the velocity of the entangled Mess after the
collision?
vf 7.59 m/s to the north
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Problem...
A grocery shopper tosses a 9 kg Bag of dog food
into a stationary 18 kg cart. The bag hits the
cart With a horizontal speed of 5.5 m/s Toward
the front of the cart. What is the final speed
of the Cart and bag?
1.8 m/s
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The law of conservation of Angular momentum
states that If no external torque acts on
an Object, then its angular momentum Does not
change.
L1 L2
I? I?
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THE END