Energy
Momentum, Collisions,
Impulse
Momentum
A
measure of how
hard it is to stop a
moving object
Momentum
=
(MASS)
(VELOCITY)
Momentum
Equation
p= m v
Units
p= mv =
(kg)(meter) =
second
kg·m
s
Momentum animations
http://physics.weber.edu/amiri/director/Mo
mentum.html
Momentum Example 1
What is the momentum of an orange
with a mass of 0.5kg
thrown with a velocity of 5.0 m/s?
m = 0.5kg
v = 5.0 m/s
p = mv = (0.5kg)(5.0 m/s) =
2.5 kg·m
s
Momentum Example 2
An object with a mass of 3.0 kg is traveling
at a velocity of 4.0 m/s .
What is its momentum?
More momentum examples
http://id.mind.net/~zona/mstm/physics/m
echanics/momentum/introductoryProblem
s/momentumSummary1.html
Conservation of Momentum
Newton’s Third Law
For every action there is an equal
and opposite reaction!
To accelerate an object, we must
apply force
Conservation of Momentum
Force(s)
must be external
Internal forces do not apply
E.g. to accelerate a car,
do you push
on the dashboard?
Conservation of Momentum
http://id.mind.net/~zona/mstm/physics/m
echanics/momentum/introductoryProblem
s/momentumSummary3.html
Collisions
Net momentum before collision =
Net momentum after the collision
Elastic Collisions
http://id.mind.net/~zona/mstm/physics/m
echanics/momentum/solvers/momentumS
olvers1.htm
Inelastic Collisions
http://id.mind.net/~zona/mstm/physics/m
echanics/momentum/solvers/momentumS
olvers1.htm
Impulse
= force exerted over time
Impulse changes momentum
Impulse
Equation
J = (Force) (time)
J = Ft
= mΔv = Δp =
m (v2-v1) = Δp
(mass)(change in velocity) =
change in momentum
Impulse
Units
J= (Newton) (seconds)
J = N·s
Force is in Newtons
Time is in seconds
Impulse Example
An 8N force acts on a 5 kg object
for 3 seconds. If the initial
velocity of the object was 25 m/s,
what is its final velocity?
F= 8 N m= 5 kg
t= 3 s
v1 = 25 m/s
v2 = ?
J = Ft =(8N)(3s) = 24 N·s
BUT we need to find v2 ………
Impulse Example
J = mΔv = m (v2-v1) =
24 N·s = 5 kg(v2 - 25 m/s) =
24 = 5 v2 - 125 m/s =
125+24= 5 v2 = 149/5 = v2 =
29.8 m/s
Impulse problems
http://id.mind.net/~zona/mstm/physics/m
echanics/momentum/introductoryProblem
s/momentumSummary2.html
0
