Download Slide 1

Momentum is a vector quantity
That is defined as the product
Of an object’s mass and velocity.
p = mv
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
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
A change in momentum
Takes force and time.
The Impulse-Momentum Theorem
FΔt = Δp
or
FΔt = mvf - mvi
Impulse (for a constant external
Force) is the product of the
Force and the time over which
It acts on an object.
FΔt is called the Impulse.
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
Stopping times and distances
Depend on the impulseMomentum theorem.
A change in momentum over
A longer time requires less force.
Angular momentum is the product
Of a rotating object’s moment
Of inertia and angular
Speed about the same axis.
L = Iω
Erica, 65kg, is spinning on a merryGo-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
The angular impulse-momentum
Theorem states that the angular
Impulse on an object is equal
To the change in the object’s
Angular momentum.
τΔt = Lf - Li
The total momentum of all objects
Interacting with one another
Remains constant regardless of
The nature of the forces
Between the objects.
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.
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
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
There are two kinds of collisions:
Those that bounce off of each other
And those that stick together
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
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
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
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
Iω = Iω