Transcript Impulse and Momentum

Impulse and Momentum
Momentum and Collisions

The goal with lesson is to understand
inertia and motion. Momentum helps
us understand collisions.

Elastic Collisions - objects rebound

Inelastic Collisions - object stick
together an usually become
distorted and generate heat
Momentum

Momentum = mass  velocity
p = mv

Momentum is a vector quantity.
Large Momentum Examples

Huge ship moving at a small velocity
P = Mv

High velocity bullet
P = mv
Momentum Examples

A large truck has more momentum
than a car moving at the same speed
because it has a greater mass.

Which is more difficult to slow
down? The car or the large truck?
Impulse

Newton’s Second Law can read
F = ma
F = m(Dv÷Dt)
F = (Dmv)÷(Dt)
F· ∆t = (Dp) ÷(∆t) ·∆t
Impulse (∆p)=FDt
When Force is Limited

Apply a force for a long
time.

Examples:
Follow through on a golf swing.
 Pushing a car.

F
Dt
Minimize the Force
Increase
Dt
 Catching
a ball
 Bungee jumping
Dt
F
Maximize Momentum Change
Apply a force for a short time.

Examples:


Boxing
Karate
F
Dt
Conservation of Momentum
This means that the momentum
doesn’t change.
 Internal forces cannot cause a
change in momentum.

Collisions
Before

v2
m1
m2

v1
After
m1

v2
m2




m1v1  m2 v2  m1v1  m2 v2
v = 10
v=0
M
M
Before Collision
p = Mv
v’ = 5
M
M
Mv = 2Mv’
v’ = ½ v
After Collision
p = 2Mv’
Conserve Energy and Momentum
Before Collision
Case 1:
Equal masses
Case 2:
M>M
Case 3:
M<M
Things I Understand…
I Need to Know more of…
Conservation in Momentum
1. A 12,000kg. railroad car is traveling at 2m/s when it strikes
another 10,000kg.railroad car that is at rest. If the cars lock
together, what is the final velocity of the two railroad cars?
2. A 9,300 kg. railroad car traveling at a velocity of 15m/s strikes
a second boxcar at rest. If the two cars stick together and move
off with a velocity of 6m/s, what is the mass of the second car?
3. A 25 gram bullet is fired from a gun with a speed of 230m/s. If
the gun has a mass of 0. 9kg. What is the recoil speed of the gun?
4. A 20 gram bullet traveling at 250m/s strikes a block of wood
that weighs 2kg. With what velocity will the block and bullet move
after the collision?
Conservation

 in Momentum


m1v1  m2 v2  m1v1  m2 v2
Impulse
Impulse=FDt
A rocket engine fires for 10 seconds
while providing 4,000 N of thrust.
What impulse is given to the rocket by
its engines?
 A 500-g baseball is given an impulse of
12.5 N-s by a baseball bat. The bat is
only in contact with the ball for 0.10
seconds. What is the average force
of the bat acting on the ball?
