Transcript 14.01.13APWeek19Momentum

Monday,
January 13, 2014
m/2
Standards: D2a1 Relate, mass,
velocity, and linear momentum for a
moving object…
Objective: SWBAT demonstrate
understanding of momentum for the
quiz.
Agenda
1. Warm Up
2. Momentum Quiz
3. Momentum Notes
4m
Warm Up
For the objects on the left,
which of the two has a
3v
greater momentum?
Which of the two will be
v/3
harder to stop?
Explain or show work for
both.
Homework
M#1
AP Physics
Tuesday 14.01.14
Standards:
D2b Relate impulse to the
change in linear momentum and
center-of-mass motion of a
system of particles
Objective: SWBAT use
knowledge of momentum and
impulse solve impulse and
stopping distance problems.
Agenda
1. Warm Up
2. Momentum & Impulse
Notes
3. Momentum & Impulse
Practice
Warm Up
Find the total momentum of
this system of objects if, a
2000 kg object has a velocity
of 2.2 m/s east, a 1700 kg
object has a velocity of 2.4
m/s south.
Homework
M#2
AP Physics
Wednesday 14.01.15
Standards: D2d Calculate the area under
a force versus time graph and relate it to
the change in momentum of an object.
Objective: SWBAT represent Impulse
graphically and interpret the physics of
the graphs they create.
Agenda
1. Warm Up
2. Review Homework
3. Impulse found graphically
4. Impulse Lab Activity
5. Begin M#3
Warm Up
1. A car of mass M, traveling at speed
V, stops in time T when maximum
braking force is applied. Assuming
the braking force is independent
of mass, what time would be
required to stop a car of mass 2M
traveling at speed V?
a) T/2 b) T c) √(2T) d) 2T e) 4T
Homework
Finish M#3
AP Physics
Thursday 14.01.16
Standards: D32&3 Identify when
linear momentum is conserved
and solve 1 d elastic & inelastic
collisions & 2D inelastic
collisions.
Objective: SWBAT understand when
linear momentum is conserved and
apply this knowledge to scenarios.
Warm Up
Graph the following data and find the
Impulse.
Δt(s)
F(N)
0.5
5
1.0
10
1.5
15
2.0
20
2.5
20
3.0
20
3.5
10
Agenda
4.0
0
1. Warm Up
2. Review M#3
Homework
3. Finish Lab
M#4
4. Conservation of Momentum Notes
AP Physics
Friday 14.01.17
Warm Up
Standards:
Estimate the impulse measured in the graph below
D32&3 Identify when linear
momentum is conserved and
solve 1 d elastic & inelastic
collisions & 2D inelastic
collisions.
Objective: SWBAT SWBAT F(N)
40
understand when linear
momentum is conserved and
20
apply this knowledge to
scenarios.
Agenda
1.
Warm Up
2.
Discussion of Lab Results
3.
Conservation of Momentum Notes
4.
Conservation of Momentum
Practice
2
1
t(s)
Homework
HW due Monday
3
Guided Practice: Stopping Distance
The most powerful tugboats in the world are built in Finland.
These boats exert a force with a magnitude of 2.85x106 N.
Suppose one of these tugboats is trying to slow a huge barge
that has a mass of 2.0x107 kg and is moving with a speed of 3.0
m/s. If the tugboat exerts its maximum force for 21s in the
direction opposite to that in which the barge is moving, what
will be the change the barge’s momentum? How far will the
barge travel before it is brought to a stop?
Momentum Quiz
1. Is momentum a scalar quantity or a vector quantity?
2. Give an example where an object’s momentum changes?
3. What physics concept that we’ve previously learned causes
an object’s momentum to change?
4. The first human-made satellite, Sputnik I, has a mass of 83.6
kg and a momentum with a magnitude of 6.63x105kgm/s.
What was the satellite’s speed?
5. The specially designed armored car that was built for Leonid
Brezhnev when he was head of the Soviet Union has a mass
of about 6.0x103 kg. Suppose this car is accelerated from
rest by a force of 8.0 kN to the east. What is the car’s
velocity after 8.0s?
Momentum M#1
1.
2.
3.
4.
(#1) In 1987, Marisa Canofoglia, of Italy, roller-skated at a recordsetting speed of 40.3 km/h. If the magnitude of Canofoglia’s
momentumwas 6.60x102 kgm/s, what was her mass?
(#3) One of the smallest planes ever flown was the Bumble Bee II,
which had a mass of 1.80x102 kg. If the pilot’s mass was 7.0x101 kg,
what was the velocity of both plane and pilot if their momentum
was 2.08x104 kgm/s to the west?
(#4) The firest human-made satellite, Sputnik I, has a mass of 83.6
kg and a momentum with a magnitude of 6.63x105 kgm/s. What
was the satellite’s speed?
(#6) In 1994, a tower 22.13 m tall was built of Lego blocks. Suppose
a block with a mass of 2.00 g is dropped from the top of this tower.
Neglecting air resistance, calculate the block’s momentum at the
instant the block hits the ground.
Impulse & Stopping Distance M#2
1 (2) A bronze statue of Buddha was completed in Tokyo in 1993. The statue is 35m
tall and has a mass of 1.00x106 kg. Suppose this statue were to be moved to a
different location . What is the magnitude of the impulse that must act on the
statue in order for the speed to increase from 0m/s to 0.20 m/s? If the magnitude
of the net force acting on the statue is 12.5 kN, how long will it take for the final
speed to be reached?
2. (5) In 1992, Dan Bozich of the United States drove a gasoline-powered gocart at a
speed of 125.5 km/h. Suppose Bozich applies the brakes upon reaching this speed.
If the combined mass of the go-cart and driver 2.00x102kg, the decelerating force is
3.60x102N opposite the cart’s motion, and the time during which deceleration
takes place is 10.0s. What is the final speed of Bozich and the go-cart?
3 (6) The “human cannonball” has long been a popular—and extremely
dangerous—circus stunt. in order for a 45 kg person to leave the cannon with the
fastest speed yet achieved by a human cannonball, a 1.6x103N force must be
exerted on that person for 0.68s. What is the record speed at which a person has
been shot from a circus cannon?
4 (2) In 1920, a 6.5x104kg meteorite was found in Africa. Suppose a meteorite with
this mass enters Earth’s atmosphere with a speed of 1.0 km/s. What is the change
in the meteorite’s momentum if the average constant force of -1.7x106N acts on
the meteorite for 30.0s? How far does the meteorite travel during this time.
5. (4) The record for the smallest dog in the world belongs to a terrier who had a
mass of only 113 g. Suppose this dog runs to the right with a speed of 2.00 m/s
when it suddenly sees a mouse. The dog becomes scared and uses its paws to
bring itself to rest in 0.80s. What is the force required to stop the dog? What is the
dog’s stopping distance?
Representing Impulse Graphically
Taking the area of an F vs Δt graph will enable you to find the
Impulse or change of momentum of a system subject to a Force.
1. Find the Impulse of the graph below
16
20
2. Find the Impulse of the graph below
16
12
F(N)
8
F(N)
12
8
4
4
0.5
1.0
1.5
Δt(s)
0.5
1.0
1.5
Δt(s)
2.0
2.5
Lab Activity –
Sketching F vs Δt graphs for various objects
Demo: Car pulling kart by string: Observe the Impulse on the spring
scale.
Activity: For a 500 g mass you will hook up a spring scale to a
motorized car, and you will drag the object for 1 meter. Complete at
least 5 trials for and average them for accuracy.
Record the total distance traveled, the total time
traveled. Record the time the scale reaches
maximum Force and the time it drops to a steady
state (constant) force.
Impulse Graph Questions M#3
1. Create a F vs Δt graph
2. Estimate the total Impulse required to speed up the object to
its constant speed.
3. What is the total Impulse required to maintain the constant
speed of the object?
4. Is the momentum actually changing when the object is
moving at a constant speed? If no, explain why our impulse is
not 0?
5. Calculate the average speed using distance/time, then using
Impulse. Compare your answers. Explain the similarities or
differences?
Conservation of Momentum
1. Kangaroos are good runners that can sustain a speed of 56
km/h (15.5 m/s). Suppose a kangaroo is sitting on a log that is
floating in a lake. When the kangaroo gets scared, she jumps off
the log with a velocity of 15 m/s toward the bank. The log
moves with a velocity of 3.8 m/s away from the bank. If the
mass of the log is 250 kg, what is the mass of the kangaroo?
Conservation of Momentum
Practice M#4
1.
2.
3.
4.
The largest grand piano in the world is really grand. Built in London, it has a
mass of 1.25x103 kg. Suppose a pianist finishes playing this piano and pushes
herself from the piano so that she rolls backwards with a speed of 1.4 m/s.
Meanwhile, the piano rolls forward so that in 4.0 s it travels 24 cm at constant
velocity. Assuming the stool that the pianist is sitting on has a negligible mass,
what is the pianist’s mass?
With a mass of 114 kg, Baby Bird is the smallest monoplane ever flown.
Suppose the Baby Bird and pilot are coasting along the runway when the pilot
jumps horizontally to the runway behind the plane. The pilot’s velocity upon
leaving he plane is 5.32 m/s backward. After the pilot jumps from the plane,
the plane coasts forward with a speed of 3.40 m/s. If the pilot’s mass equals
60.0 kg, what is the velocity of the plane and pilot before the pilot jumps.
The largest frog ever found was discovered in Cameroon in 1989. The frog’s
mass was nearly 3.6 kg. Suppose this frog is placed on a skateboard with a
mass of 3.0 kg. The frog jumps horizontally off the skateboard to the right,
and the skateboard rolls freely in the opposite direction with a speed of 2.0
m/s relative to the ground. If the frog and skateboard are initially at rest,
what is the initial horizontal velocity of the frog?
In 1994, ,a pumpkin with a mass of 449 kg was grown in Canada. Suppose you
want to push a pumpkin with this mass along a smooth, horizontal ramp. You
give the pumpkin a good push, only to find yourself sliding backwards at a
speed of 4.0 m/s. How far will the pumpkin slide 3.0 s after the push?
Assume your mass to be 60.0 kg.
Perfectly inelastic collisions
vb
vr
` `
` `
` `
Before
` `
vbr
``
` `` `
``
After
Elastic is like a rubber band. It stretches, it pushes back on you or
bounces back, like a spring. So an inelastic collision is a collision where
there is no bounce. In this case, there is a crunch.
-Momentum is conserved during inelastic collisions, even though
mechanical energy is not conserved in this situation. Why do you
think mechanical energy is not conserved in inelastic
collisions? Where does the energy go?
Elastic Collisions
vb
vr
``
``
Before
``
``
vb
vr
``
``
``
``
After
In elastic collisions the two objects bounce off each other with no
mechanical energy lost to heat, sound, or deformation of the object.
When no external force is present momentum is conserved so:
mrvri+mbvbi=mrvrf+mvbf