do now: who was the best teacher you ever had? what was it about that person and their class that...
TRANSCRIPT
Do Now:Who was the best teacher you ever
had?What was it about that person and
their class that made an impact on you?
BrainstormingWhat does the word
“momentum” mean to you?What about “impulse?How have you used these two
words in your life?
Do Now (1/3/12):1.What does the word
“momentum” mean to you?2.What about “impulse?3.What was the best thing
about your break?Happy New Year
Momentum1/3/11LAST TOPIC OF THE SEMESTER!!!
Linear Momentum:Linear Momentum: the product of
the mass and velocity of an object; represented by the symbol p (units: kg x m/s); is a vector quantity
mvp
Example:Anquan Boldin has a mass of 130
kg. If he runs east at 35 m/s, what is the magnitude and direction of his momentum?
Example:Anquan Boldin has a mass of 130
kg. If he can run at the same speed as Haloti Ngata, who has a mass of 200 kg, who has the greater momentum?
Impulse-Momentum Theorem:The impulse on an object is
equal to the change in momentum it causes
if
if
pptF
mvmvvmtF
Example: Stopping a vehicleA 2200 kg SUV traveling at 94
km/h (26 m/s) can be stopped in a. 21 s by gently applying the
brakesb. 5.5 s in a panic stopc. 0.22 s if it hits a concrete wallFind the average force exerted in
each case.
Practice:Use the rest of class to work on
“Intro to Momentum.” It is due tomorrow!
#4 = “km/h” should be “m/s”
Do Now (1/4/12):
1. A 2400 kg SUV and a 1300 kg sports car are traveling at the same speed. Which one has the greater momentum?
2. If they are both traveling at 20 m/s, what is the momentum of each?
Pass In:Momentum homework (half-
sheet)Last week’s Do Now’s (if you
haven’t already)Home Alone Extra Credit (if you
haven’t already)
Collisions and Conservation of Momentum1/4/11: Inelastic Collisions
Systems:Closed system: a system which
does not gain or lose massIsolated system: a system with a
net external force equal to zero
The Law of Conservation of Momentum
The momentum of any closed isolated system does not change
fi pp
Types of Collisions:Elastic: objects do not stick
together after collisions Inelastic: objects stick together
after collisionhttp://www.physicsclassroom.co
m/mmedia/momentum/creti.cfm
Inelastic Collision
Objects sticking together after collision will have the same velocity:
fii
ffii
vmmvmvm
vmvmvmvm
)( 212211
212211
fi pp
Take a collision between two objects (m1 and m2). Use Conservation of Momentum:
Example:A 1875 kg car going 23 m/s rear
ends a 1025 kg compact car going 17 m/s on ice in the same direction. The two cars stick together. How fast do the two cars travel together after the collision?
Elastic CollisionsObjects do not stick together; the
objects do not have the same final velocity
ffii vmvmvmvm 22112211
Example: #2 on back of homework:Work with your seatmate to list
the variables in this problem.Determine whether the collision
is elastic or inelastic.
Practice:Use the rest of class to work on
the worksheet “Collisions and Conservation of Momentum.”
Elastic Collisions1/5/11
Do Now:A 1875 kg car going 23 m/s
rear ends a 1025 kg compact car initially at rest on ice in the same direction. The two cars stick together.
1. What type of collision is this?
2. How fast do the two cars travel together after the collision?
Recoil:Both objects start out at rest (both
vi are 0)
ff
ff
ffii
vmvm
vmvm
vmvmvmvm
2211
2211
22112211
0
Examples of recoil: ExplosionA diver shooting a gun in the
waterIce skaters pushing one anotherAn astronaut throwing something
in space
Example:An astronaut at rest in space
fires a thruster pistol that expels 3.5 kg of gas at 875 m/s. The combined mass of the astronaut and the pistol is 84 kg.
How fast and in what direction is the astronaut moving after firing the pistol?
Practice:Please use the rest of class to
work on one of three things:1. Your homework2. Your notecard for your quiz
tomorrow3. Your final materials list (if
needed)
Do Now:Two ice-skaters are at rest on the
ice. The ice skater with a mass of 70 kg pushes 50 kg skater, who recoils with a speed of -12 m/s. How fast and in what direction is the70 kg skater moving?
Classwork:
Please work on one of three things only:
HomeworkIn classroom textbooks: pick 4
problems from each set:◦P. 218: #22-28◦P.219 #34-40
Work on your notecard!
Do Now:
1. What two types of collisions are there?
2. What are the steps for solving momentum problems?
3. Turn in your hw and Do Now’s (you should have six)!!!
Steps: Sketch the Problem Sketch the problem before and after the
event using vectors, including an axis indicating the positive and negative directions
+
Vi=26 m/s Vf=0 m/s
Steps: List Knowns and Unknowns:Knowns:m=2200 kgvi=26 m/s
vf=0 m/s
∆t=21s, 5.5s, 0.22sUnknowns:F=?
Steps: CalculationDetermine the momentum before
and afterApply impulse-momentum
theorem to calculate force