Objective SWBAT recall, explain, and solve problems that test
knowledge of physics concepts.
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Todays Agenda Conservation of Momentum Review Review
Exercise
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Why Conservation of Momentum? Objective: SWBAT solve
conservation of momentum problems. 68.8% 83%
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The Concept Conservation = Nothing is lost, nothing is gained.
Usually we are talking about before a collision And after a
crash
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The Concept Before mv + = + P = MV
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The Concept So, this notation that you see: p i = p f It means
the total amount of momentum before a collision equals the total
amount of momentum after the collision. Other ways we can write
this: m i v i + m i v i = m f v f + m f v f m i v i + m i v i = (m
f + m f )v f Object 1 Object 2Object 1Object 2
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Two bowling balls are rolling towards each other on ice (assume
no friction). Ball A has a mass of 5 kg and is moving to the right
at 10 m/s. Ball B has a mass of 7 kg and is moving at 7 m/s. If the
balls stick together after the collision, how fast do they move
after they collide? 5 kg, 10 m/s AB 7 kg, -7 m/s
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An air hockey puck (5kg) is moving at 8 m/s collides with
another air hockey puck moving at 8 m/s. After the collision, both
pucks are at rest. What is the mass of the second puck?
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An air hockey puck (5kg) moving at 8 m/s collides with another
air hockey puck moving at 8 m/s. After the collision, both pucks
are at rest. What is the mass of the second puck?
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You Try 2 Practice Problems We will then quickly go over them
Following this, we will begin our review game!
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Two bowling balls are traveling towards each other in outer
space where there is no friction. Ball A has a mass of 9 kg and is
moving in the positive direction at 14 m/s. Ball B has a mass of 4
kg and is moving at 6 m/s. If the balls stick together after the
collision, how fast do they move after they collide? 9 kg, 14 m/s
AB 4 kg, -6 m/s
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A large truck (256 kg) is traveling east down the road at a
speed of 54 m/s. It collides with a small car (134 kg) that is also
traveling east, but slower, going only 12 m/s. If the two cars
stick together after the collision, how fast are they moving?
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Distributing Envelopes Everyone gets one. Dont open it until
everyone has one!
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Do Now: Split Up FRONT BACK MIT HARVARD
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The Central Square Battle The Harvard Crimson versus The MIT
Beavers Note: no longer mascot
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Why The Battle? To fight over getting the highest grade on
their midterms.
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How Will They be Fighting? By a good old-fashioned game of
Bluff.
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How Does Bluff Work? Say Harvard is up first. A question will
come up on the slideshow. Is velocity a vector or scalar quantity?
Harvard students will be given a certain amount of time to come up
with the answer. On their own, of course. Velocity is a vector,
because it has direction. When times up, every Harvard student that
thinks they know the answer can stand up.
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So, now we have a bunch of Harvard kids standing around, that
apparently know the answer. Ill randomly choose 1 MIT kid. He can
choose any Harvard kid to share their answer. If he gets it right,
Harvard gets a point for each person who was standing. If hes
wrong, any MIT student can give me the answer. If hes right MIT
gets the same # of points. How Does Bluff Work?
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How Does Bluff Work No talking during problem-solving time.
Minus 5 point penalty. You get to celebrate! For 10 seconds each
round after you get 1 right. No talking during how-to-do-it time. I
will quickly show how to solve Minus 5 point penalty. Winners???
Get a prize? What is it? Wait and see!
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How Does Bluff Work? Whos going to win, Harvard or MIT?
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First Team Up Harvard University! So they will solve problem I
will choose a person from MIT to pick the Harvard person to share
their answer. MIT should solve too! If Harvard gets it wrong you
get a shot!
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Silence Warning Remember to be silent during problem solving
time!
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Question 1 A 2 kg hockey puck is moving at 9m/s, how much
momentum does the hockey puck have?
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Question 2 A 100 kg car is traveling at 20 m/s. It then speeds
up to 40 m/s. Calculate the impulse.
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Question 3 A 20 kg bear is running at 10 m/s towards an
unsuspecting 50 kg person who is not moving. They collide. If the
bear and person stick together, what will their final velocity
be?
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Question 4 A 32 kg ice skater is traveling at +45 m/s towards a
5 kg hockey goal that is at rest. After she collides with the goal
(they do not stick together), the goal moves with a speed of +36
m/s. What is the final velocity of the ice skater?
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Question 1 A car travels a distance of 12 meters in 4 seconds.
What is its average velocity during this trip?
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Question 2 Is mass scalar or vector? No direction to mass! Its
scalar!
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Question 3 A rock is sitting on top of a cliff with 30 Joules
of gravitational potential energy (GPE). The rock then falls off
the cliff and hits the ground. As it hits the ground, how much KE
does the rock have in Joules? SWBAT solve conservation of Energy
Problems Energy is conserved. So, the energy in the beginning,
equals the energy at the end! 30 in the beginning, means 30 at the
end!
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Question 4 If a 7 Newton force is applied over 2 meters, how
much work is done? SWBAT solve conservation of Energy Problems
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Question 5 A boy tugs a sled with a string. He pulls it with a
15 N force for a distance of 6 meters. The string is at a 25 0
degree above the horizontal and sled slides along the flat
ground.
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Question 6 A person holds a 8 kg box above his head by applying
a 6 N force as he walks down the street a distance of 12 meters.
How much work does the person do on the box? Force Distance
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Question 7 A car is traveling at 5 meters per second. The car
then accelerates at a rate of 2 m/s 2 for 2 seconds. What is the
cars final velocity?
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Question 8 What is x is equal to? 35 meters x 42 0
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Question 9 Paul wants to see if running lowers blood pressure.
Paul has 10 friends run 1 mile everyday for a year and 10 friends
not run for a year. All 20 participants eat the same exact diet and
exercise the same amount besides the running. Afterwards, he
measures their blood pressure. What is the independent variable in
this experiment? Running
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Question 10 Paul wants to see if running lowers blood pressure.
Paul has 10 friends run 1 mile everyday for a year and 10 friends
not run for a year. All 20 participants eat the same exact diet and
exercise the same amount besides the running. Afterwards, he
measures their blood pressure. What is a control variable in this
experiment? Diet, exercise besides running
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Question 11 Convert 10 meters per second into kilometers per
second.
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Question 12 Convert 45 days into hours.
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Question 13 Convert 34 kilometers per hour into meters per
second.
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Question 14 Convert 34 centimeters per second into meters per
hour.
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Question 15 Larry walks 56 meters North and then 24 meters
South, what is Larrys distance traveled?
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Question 16 Gary walks 22 meters North and then 42 meters
South, what is Garys displacement?
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Question 17 A car constantly accelerates from rest to a speed
of 84 meters per second in 4 seconds. What is the cars
acceleration?
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Question 18 A truck traveling at 34 m/s slams on its breaks and
comes to rest in 4 seconds. During this 4 seconds, that truck
travels 94 meters. What is the trucks acceleration during this
period?
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Question 19 A ball is thrown straight upwards. At its highest
point, what is its velocity equal to?
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Question 20 A ball is thrown straight upwards, at its highest
point, what is its acceleration equal to? Acceleration due to
gravity is constant = -9.81m/s 2
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Question 21 A hockey puck is hit off of the edge of a cliff. As
it leaves the cliff, it is moving exactly horizontally with a speed
of 5 meters per second. Two seconds later it is falling through the
air. At this moment, what is its horizontal speed equal to?
Horizontal speed is constant. So = 5m/s
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Question 22 A ball is dropped off a 34 meter bridge. When it
hits the ground, what is its velocity equal to?
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Question 23 I push against a wall with a force of 54 N and it
doesnt move. What is the force against me provided by the wall?
Newtons Third Law: Equal and Opposite, so 54N
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Question 24 A 4 kg textbook sits on the floor. What is the
normal force provided by the floor?
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Question 25 A boat, sitting on the earth, has a mass of 65 kg.
What is its weight?
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Question 26 A person pulls on a book to the right with a force
of 56 N, another person pulls the book to the left with a force of
86 N, what is the net force on the book?
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Question 27 A vehicle has a mass of 54 kg. The vehicle
accelerates at a rate of 12 m/s 2 for 3 s. What is the net force on
the ball during acceleration?
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Question 28 As a worker for Van Houtens moving company, you
have to push some furniture around. You push on a table with a
force of 400 N, but it doesnt move. What type of friction causes
the table not to move? Static Friction! Remember, Static means
Still
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Question 29 Youre pushing on the table with a force of 25N when
it doesnt move. Now, you push harder, with a force of 45N, but the
table still doesnt move. What is the Frictional Force equal to at
this time? 45 N If something isnt moving, that means the force are
balanced. 45N
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Question 30 Which is greater, kinetic friction or static
friction? Static! Its harder to get something started, then to keep
it moving!
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Question 31 Which is greater, s or k ? s, which means static!
Its harder to get something started, then to keep it moving!
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Question 32 Your grandfather tells you to push a 25 kg
microwave across the counter so he can heat up his Hot Pocket. If
the coefficient of kinetic friction is.25 and the coefficient of
static friction is.30, how hard do you have to push to get the
couch to begin moving?
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Question 33 You are pushing a 45kg wheelchair down the road
with an acceleration of 4 m/s 2, in order to do this you are
pushing with a force of 220 N. What is the coefficient of kinetic
friction between the road and the wheelchair?
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Question 34 A 25kg dog is launched out of a canon with a speed
of 45 m/s. What is the dogs momentum equal to?
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Question 35 A horse and buggy initially has 200 kg x m/s of
momentum. It crashes into a McDonalds and comes to a complete stop.
If the collision takes 1.25 seconds, what is the average force on
the horse and buggy?
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Question 36 A 3 kg dart is on a spring that is at ground level.
The spring is compressed 0.65 meters and the ball is then shot up
into the air. If the ball reaches a peak height of 9 meters, what
is spring constant of the spring equal to?
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Question 37 A ball is dropped off a bridge with a height of 56
meters. What will its speed be when it hits the ground?
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Importantly Use the Study Guide to help you. Practice solving
the problems on your own and then check your answers. USE THE BLOG
www.phaphysics.wordpress.com USE THE DISCUSSION BOARD FOR HELP