p250c1

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Chapter 7 Linear Momentum
Momentum a measure of motion Force a cause of
change in motion What changes when a force is
applied?
Linear Momentum p mv (vector!!!!!) the
tendency of an object to pursue straight line
motion Kinetic Energy in terms of momentum
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Impulse the change in motion
Example A baseball with mass 0.14 kg and an
initial speed of 30 m/s his hit with a bat and
then rebounds in the opposite direction at a
speed of 40 m/s. The bat and ball are in contact
for 0.0020 s. Determine the size of the impulse
on the ball and the magnitude of the average
force of the bat on the ball.
3
Example A 51 kg teenager jumps to the ground
from a chair 0.34 m high. She bends her knees
slightly on landing, lowering herself by only 8.0
cm during her landing. What is the average force
with which her feet hit the ground?
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Conservation of momentum two bodies
action/reaction no other forces FAB - FBA
gt equal but opposite impulses gt DpA DpB
0 When the net external force on a system is
zero, the total momentum of that system is
constant. p1 p2 p3 ... is
constant Collisions m1v1 m2v2 m1v1 m1v2

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Example A Buick Park Avenue (m1660 kg) with an
initial speed of 8.0 km/hr collides head on with
a Geo Metro (m830 kg). As a result of the
collision, the cars become entangled and so sick
together. - What is the speed of the wreckage
just after the collision? - How do the
accelerations of each car compare? (look at the
changes in their velocities)
Example A 60 kg ice skater initially at rest
throws a 2 kg block of ice horizontally with a
speed of 12 m/s. What is his recoil velocity?
Ballistic Pendulum demo
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Collisions Elastic Collisions conserve KE (total
KE is same before and after collision) Inelastic
Collisions some KE is lost during collision
(heat, sound, etc.) Completely Inelastic
Collisions objects stick together maximum
possible loss of KE In all collisions, the total
momentum is conserved!
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Collisions m1v1 m2v2 m1v1 m1v2 in 2 or
3 dimensions take components! m1vx1 m2vx2
m1vx1 m1vx2 m1vy1 m2vy2 m1vy1 m1vy2
Example Two cars approach an intersection at
right angles. After the crash they stick
together. If one car has a mass of 1450 kg and
is traveling north at 11.5 m/s and the other has
a mass pf 1750 kg and is traveling east at 15.5
m/s, determine the speed and direction of motion
of the wreckage just after the collision.
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Example A billiard ball moving at 10 m/s along
the positive x axis collides with an identical
billiard ball at rest. After the collision, the
incoming ball moves at a speed of 7.7 m/s at an
angle 40º from the x axis. What is the speed and
direction of the struck ball?