Download Momentum PPT

Momentum &
Collisions
Physics - Chapter 6
Momentum
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Vector quantity
Product of an objects mass and velocity
Represented by p
SI units of kg x m/s
Momentum is what makes it hard to stop
an object rolling down a hill
 P=mxv
A 2250 kg pickup truck
has a velocity of 25 m/s to
the east. What is the
momentum of the truck?
Changes in momentum
 A force applied for a certain time will
cause a change in momentum
 Impulse-momentum theorem
FΔt = Δp
or
FΔt = Δp = mvf - mvi
A 1400 kg car moving
westward with a velocity of
15 m/s collides with a utility
pole and is brought to rest in
0.30 s. Find the force
exerted on the car during the
collision.
A 2240 kg car traveling to
the west slows down
uniformly from 20.0 m/s to
5.00 m/s. How long does
it take the car to
decelerate if the force on
the car is 8410 N to the
east?
Law of Conservation of
Momentum
 The total momentum of all objects
interacting with one another remains
constant.
 In equation form:
m1v1,i+m2v2,i = m1v1,f+m2v2,f
total initial momentum = total final momentum
A 76 kg boater, initially at
rest in a stationary 45 kg
boat, steps out of the boat
and onto the dock. IF the
boater moves out of the boat
with a velocity of 2.5 m/s to
the right, what is the final
velocity of the boat?
Perfectly Inelastic
Collisions
 A collision in which two objects stick
together and move with a common
velocity after colliding
 Equation for a perfectly inelastic collision
m1v1+m2v2=(m1+m2)vf
 Be careful with signs for velocity!
 Kinetic energy is not conserved
Elastic Collisions
 A collision in which the total momentum
and the total kinetic energy remain
constant
 After the collision, the two objects move
separately
In real life…
 Only particle collisions are truly
considered elastic, however, some
collisions are close enough to be
approximated as elastic
 Most collisions are somewhere between
being elastic and perfectly inelastic
A 1850 kg luxury sedan stopped at a
traffic light is struck from the rear
by a compact car with a mass of 975
kg. The two cars become entangled
as a result of the collision. If the
compact car was moving at a
velocity of 22.0 m/s to the north
before the collision, what is the
velocity of the entangled mass after
the collision?
A 0.015 kg marble moving to the
right at 0.225 m/s makes an elastic
head-on collision with a 0.030 kg
shooter marble moving to the left at
0.180 m/s. After the collision, the
smaller marble moves to the left at
0.315 m/s. Neglect friction. What is
the velocity of the 0.030 kg marble
after the collision?