Download 0 of 20 - BHSPhysics

Project
 View
the several objects on the
designated lab tables.
 Which of these objects contain energy?
What type of energy do they contain?
 Which of these objects contain no energy?
 Based on your answers, what would be
your definition of energy?
Lesson #58
Topic: Intro to Energy
Objectives:
(After this class I will be able to)
1. Describe different types of energy.
3/5/07
Which of the following objects does
not contain any energy?
B
A
0 of 20
0%
0%
at
te
ll
ry
oo
of
d
th
bl
es
oc
e
k
th
in
gs
c.
.
0%
W
ub
R
0%
ba
nd
0%
le
0%
R
6.
be
r
5.
pp
4.
A
3.
k
2.
Rock
Apple
Rubber band
Battery
Wood block
All of these things
can have energy.
oc
1.
Which of the following statements is
most true about energy?
er
gy
er
gy
cr
e.
..
..
be
ca
nn
ot
so
m
et
hi
ng
r..
.
th
at
a
le
s
rt
ic
is
En
O
nl
y
pa
nl
y
O
0 of 20
pa
rt
ic
le
s
4.
0% 0% 0% 0%
En
3.
m
...
2.
Only particles with
mass have energy.
Only particles that are
moving have energy.
Energy is something
we are running out of.
Energy cannot be
created or destroyed.
w
ith
1.
Which of the following are mostly
related to “Mechanical” Energy?
...
tr
ic
nd
C
tia
la
d
Po
te
n
an
tic
in
e
K
El
ec
he
m
ic
El
e
nd
al
...
..
ct
ric
l..
.
la
C
he
tic
in
e
K
0 of 20
m
ic
a
an
4.
0% 0% 0% 0%
nt
ia
3.
Po
te
2.
Kinetic and
Potential energy
Chemical and
Electrical energy
Kinetic and
Chemical energy
Potential and
Electric energy
d
1.
Project
 Split
up into groups and research the
following questions.
 What is energy?
 How is energy used?
 Where does energy come from?
 List five ways we need energy to live.
 List five different sources of energy.
 Describe a transfer of energy from start to
finish.
Lesson #59
Topic: Work and Potential Energy
Objectives: (After this class I will be able to)
2/13/07
1. Describe the relationship between
work and energy.
Warm Up: Warm Up: When / how do you do work?
Assignment: Ch 10 p 261 #1- 3
Which is an example of doing work
onto a book?
a.
..
t..
Th
ok
bo
ro
w
in
g
th
e
ng
ck
i
Pi
th
e
bo
co
ns
ok
ta
n
of
f
t.
..
...
at
in
g
al
k
W
H
0 of 20
ol
di
ng
th
e
4.
0% 0% 0% 0%
ab
3.
k
2.
Holding the book
above your head.
Walking at constant
speed with the book.
Picking the book off
the floor and setting
it back down.
Throwing the book
across the room.
bo
o
1.
Work and Energy

Work is done when an objects velocity or position is
changed.
 A force, F, was exerted on an object while the object
moved a distance, d, as shown in the figure.

Work is equal to a constant force exerted on an object
in the direction of motion, times the object’s
displacement.
Work and Energy Experiment

Create a stack of books 5 books high.

Use a force sensor to measure the force needed to lift a cart to
the top of the books. Record this force.

Measure the distance the cart traveled. Record this distance.

Repeat these procedures using a steep ramp to raise the cart
to the top of the books. Record the distance the cart moves
and the force required to move it.

Perform 3 more trials, each time making the ramp less and less
steep. Continue to record all data.

Multiply the force times the distance moved for each trial.

Analyze your results. Can you predict how much force it would
require to raise the cart to the top of the books if the ramp was
2m long?
Work and Energy

Consider a force exerted on an object while the object
moves a certain distance. Because there is a net force,
the object will be accelerated, a = F/m, and its velocity
will increase.

In the equation 2ad = vf2 − vi2 , if you use Newton’s
second law to replace a with F/m and multiply both
sides by m/2, you obtain:

The energy resulting from motion is called kinetic
energy and is represented by the symbol KE.
Work and Energy
 Substituting KE into the equation
results in W = KEf − KEi.
 The right side is the difference, or change, in kinetic
energy.
 The work-energy theorem states that when work is
done on an object, the result is a change in kinetic
energy.
 The work-energy theorem can be represented by the
following equation.
 Work is equal to the change in kinetic energy.
Using the previous equations, what
are the units of Work?
0%
0%
m
m
2
0%
N
N
0 of 20
m
0%
g
4.
K
3.
/m
2.
Nm
N m2
N/m
Kg m
N
1.
Using the previous equations what
are the units of kinetic energy?
..
un
m
th
e
as
m
e
sa
e
Th
0 of 20
its
.
2
N
m
2/
K
g
m
N
2/
s
0% 0% 0% 0% 0%
2/
s2
5.
m
/s
4.
g
3.
K
2.
N m2/s2
Kg m2/s2
Kg m/s2
N m2/s
The same as the
units for work.
s2
1.
Work and Energy

We call the abnormally large unit of energy a Joule

1J = 1 N m = 1kg m2/s2

Lifting a 1N apple 2 meters above the ground requires 2
Joules of work / energy.

Through the process of doing work, energy can move
between the external world and the system.

The direction of energy transfer can go both ways. If the
external world does work on a system, then W is positive
and the energy of the system increases.

If, however, a system does work on the external world,
then W is negative and the energy of the system
decreases.
Two identical cannons each fire the
same cannon ball. Which cannon
will fire farther?
sh
e
Th
Th
0 of 20
e
id
ea
ce
c.
..
no
e
av
ba
rr
el
ta
n
Ih
lo
ng
or
te
r
er
ba
rr
e
lc
...
4.
0% 0% 0% 0%
di
s
3.
m
e
2.
The longer barrel
cannon
The shorter barrel
cannon
Same distance
I have no idea
Sa
1.
Work Examples:

Each cannon ball exerts the same amount
of force, however the longer barrel will exert
that force for a longer distance.
 The longer barrel cannon does more work
onto the cannon ball.
 This results in a greater change in kinetic
energy of the cannon ball.
 Greater kinetic energy is equivalent to
greater velocity.
Calculating Work
 Work
can be done by each force acting on
an object.
 The total work done onto an object is the
sum of all the work done by each
individual force acting on the object.
 You can also find the total work done by
finding the net force acting on an object
and multiplying it by the object’s
displacement.
Work Examples

Example #1: A student lifts a 1kg book 1m off of
the floor at constant speed.
 What is the total work done onto the book?

What is the work done onto the book by the
student?

What is the work done onto the book by gravity?
Work Examples

Example #2: The student then begins walking 30m
down the hall to his next class. His steady walking
speed through the hall is 2m/s.
 What is the work done onto the book by the student
when he begins to walk?

What is the work done onto the book by the student
when he slows down to a stop?

What is the total work done onto the book from being at
rest in the first class to being at rest in the second
class?
Work Examples

Example #3: The student then sets his book
down onto the floor next to his desk in the
second class. He lowers the1kg book 1m at
constant speed.
 What is the total work done onto the book?

What is the work done onto the book by the
student?

What is the work done onto the book by gravity?
Calculating work
Calculating Work


Other agents exert forces on the pushed car as well.
Earth’s gravity acts downward, the ground exerts a
normal force upward, and friction exerts a horizontal
force opposite the direction of motion.
 The upward and
downward forces are
perpendicular to the
direction of motion and
do no work. For these
forces, θ = 90°, which
makes cos θ = 0, and
thus, W = 0.
Calculating Work

The work done by friction acts in the direction
opposite that of motion—at an angle of 180°.
Because cos 180° = −1, the work done by
friction is negative.

Negative work done by a force exerted by
something in the external world reduces the
kinetic energy of the system.

Positive work done
by a force increases
the kinetic energy.
A 105-g hockey puck is sliding across the ice. A player
exerts a constant 4.50-N force over a distance of 0.150 m.
How much work does the player do on the puck? What is
the change in the puck’s energy?
0%
0%
0%
57
J
01
5J
67
0.
6.
0 of 20
75
J
0%
0.
4.
5J
3.
.7
2.
6.75J
0.675J
15.75J
0.0157J
15
1.
If you ride a bicycle on a 100-m long road
inclined at 25°, applying a constant force of
40 N, find the work done by you.
(40 N) (100 m)
(40 N) (100 m) sin 25°
(40 N) (100 m) cos 25°
(40 N) (100 m) tan 25°
0%
m
)t
an
25
25
°
10
0
)(
N
0
N
0
(4
(4
0
N
)(
)(
10
0
10
0
m
)c
m
)s
os
in
25
m
)
10
0
)(
N
0
(4
0 of 20
0%
°
0%
°
0%
(4
A.
B.
C.
D.
A 4-N soccer ball sits motionless on a field. A player’s foot
exerts a force of 5 N on the ball for a distance of 0.1 m, and
the ball rolls a distance of 10 m. How much kinetic energy
does the ball gain from the player?
0%
0%
J
0%
J
0%
J
0 of 20
0.5 J
0.9 J
9J
.05 J
J
A.
B.
C.
D.
The diagram shows a box being pulled by a rope
with a force of 200.0 N along a horizontal surface.
The angle the rope makes with the horizontal is
45°. Calculate the work done on the box to pull it a
distance of 5.0 m.
1. 52.5J
2. 250J
3. 525J
4. 707J
20
0%
0%
0%
0%
0
7J
70
5J
52
0J
25
52
.5
J
0
Bonus Activity Description




You will receive 1 bonus point per M&M
consumed and burned off (10 M&M limit).
Example: You choose to eat 4 M&M’s and you
answer all questions accurately and burn off all
4 M&M’s by the end of the period, you will
receive 4 bonus points.
However, you must burn off all consumed
energy by the end of the period. Failing to do
so will result in zero bonus points.
Example: Eating 4 M&M’s and only burning off
3 of them by the end of the period.
Bonus Activity
 We
eat food everyday to gain potential
energy.
 We then use this energy on doing work.
 Today you will see how much work you
have to do to use all of the potential
energy of the food you eat.
 On a separate sheet of paper, answer the
following questions.
Bonus Activity
1.
2.
3.
4.
How many M&M’s would you like to eat?
There are 210 food Calories in ¼ cup of
M&M’s. If there are 48 M&M’s in ¼ cup,
How many food calories are in 1 M&M?
If there are 1000 heat calories in 1 food
calorie, how many heat calories are in 1
M&M?
If there is 4.185 Joules of energy in 1
heat calorie, how many Joules of energy
are in 1 M&M?
Bonus Activity
5.
6.
7.
8.
How many Joules of potential energy did
you just consume?
What is your mass in kilograms? (divide
your weight in pounds by 2.2)
How much work is done by lifting your
weight 0.45 meters? (the height of your
chair)
How many times do you have to step up
onto your chair to burn off the M&M’s?
(Divide the answer to #5 by the answer
to #7)
Project
 Explain
the transfer of energy of a block
falling to the floor.
 What is doing work when the block is
falling?
 What is doing work when the block hits the
ground?
 How does the kinetic energy of the block
change from beginning to end?
Lesson #60
Topic: Gravitational PE
Objectives:
1.
3/19/07
(After this class I will be able to)
Describe gravitational potential energy.
Warm Up: #1 What is the equation for the amount of work a
force does on an object?
#2 What is the equation for the total work done onto an
object?
#3 If an object starts from rest and finishes at rest, what is the
total work done onto the object?
#4 What is the total work done on an object moving at
constant speed?
Assignment: “Section 10 -1 quiz” due tomorrow
What is the equation for the
amount of work a force does on an
object?
1.
2.
3.
4.
W=Fd
W=Fdcosθ
W=ΔKE
W= 0.5mv2
0 of 20
What is the equation for the total
work done onto an object?
1.
2.
3.
4.
W=Fd
W=Fdcosθ
W=ΔKE
W=0.5mv2
0 of 20
If an object starts at rest and
finishes at rest, what is the total
work done onto the object?
w
or
k
se
of
J
0
of
ot
h
B
th
e
on
en
ds
ep
D
0 of 20
th
e
...
fo
rc
e
t..
.
di
s
th
e
on
4.
0% 0% 0% 0%
en
ds
3.
ep
2.
Depends on the
distance moved
Depends on the
force acting on it
Both of these
0 J of work
D
1.
If an object is moving at constant
speed, what is the total work done
onto the object?
se
of
J
0
of
ot
h
B
th
e
on
en
ds
th
e
...
fo
rc
e
t..
.
di
s
th
e
0 of 20
w
or
k
0% 0% 0% 0%
ep
4.
on
3.
en
ds
2.
Depends on the
distance moved
Depends on the
force acting on it
Both of these
0 J of work
ep
1.
Potential Energy






An object that has the ability to do something
has potential energy.
A block at rest on a 1m high desk has the
potential to fall due to the force of gravity.
If the block has a mass of 1kg, gravity could
“potentially” do ______ J of work onto the block.
This is how much Gravitational potential
energy the block has while at rest on top of the
desk.
A common shortcut to find the gravitational PE
of an object is PEg=mgh.
Where h is the objects height above the ground.
What is the gravitational potential
energy of a 20kg boulder sitting on
a 50m high cliff?
00
J
0%
J
0%
,0
0N
20
0%
0
0%
0 of 20
10
4.
0J
3.
00
2.
200N
1,000J
10,000J
0J
1,
1.
A 1000kg car is at the top of an 30°
incline that is 40m long. What is the
car’s gravitational potential energy?
1.
2.
3.
4.
20,000J
40,000J
200,000J
400,000J
0%
0%
0%
0%
J
40
0,
00
0
J
20
0,
00
0
00
J
,0
40
20
,0
00
J
0 of 20
Project
 With
your partner, create a list of simple or
complex machines you use daily.
 Do you think these machines are efficient
or inefficient? (in terms of energy put in
and work that gets done.)
Lesson #61
Topic: Machines, Power, and Efficiency
Objectives:
1.
3/20/07
(After this class I will be able to)
Explain what makes a machine efficient
and powerful.
Warm Up: #1 How does a ramp make it easier to lift an
object? What other simple machines could be used to lift a
heavy object?
Assignment: “Machines and Power” due Thursday
Simple Machines

1.
2.
3.
You wish to lift a 100kg crate into the bed
of a pickup that is 1.5m above the
ground. Explain how the following
machines makes this task easier.
Push the crate up a ramp.
Use a fulcrum and lever.
Use a pulley system.
Simple Machines
Example #1
1. Push the crate up a ramp.
The crate is 100kg, the height of the truck is
1.5m, the length of the ramp is 10m. How
much force do you have to exert to push the
crate up the ramp?
Simple Machines
Example #2
2. Use a lever and fulcrum.
The crate is 100kg, the height of the truck is
1.5m, you push the opposite end of a lever
down 10m. With how much force do you
have to push down on the opposite end of
the lever?
You use a pulley system such that you pull
10m of rope out of the pulley system to lift
the crate. How much force do you have to
exert onto the rope? (Example #3)
0 of 20
0N
0%
15
0J
00
0%
15
0%
J
0%
15
4.
N
3.
00
2.
1500N
1500J
150J
150N
15
1.
Efficiency
 This
example is true for ideal situations,
however no machine is 100% efficient.
 In all of the previous examples, we would
have to exert more than 150N because the
efficiency of the machines would be less
than 100%
 The amount of ideal work done compared
to the amount of actual work done is the
machines efficiency.
 % efficiency = ideal / actual * 100
Efficiency
 When
using the ramp, the actual force
exerted pushing the crate was 200N. What
is the % efficiency of the ramp?
The efficiency of the pulley system used to
lift the crate is 50%. What was the actual
force exerted onto the rope?
0%
0N
0N
0%
30
0 of 20
0%
20
0%
N
4.
75
3.
0N
2.
150N
75N
200N
300N
15
1.
Project
 Vote
on the most powerful person in the
class.
 The top 5 will compete in several different
competitions.
 Based on the competitions, who do you
think was most powerful?
 Why?
Power

Power is the rate in which work is done onto an
object.
 A powerful machine is one that can do a large
quantity of work onto an object in a short amount
of time.
Work
Power 
time
W Fd
P

 Fv
t
t
Ron and Stan are both 2m tall. Ron can lift
40kg over his head in 2 seconds. Stan can
lift 30kg over his head in 1 second. Who is
more powerful?
1. Ron
2. Stan
3. They’re the same
4. Not enough info.
0%
in
fo
.
0%
ug
h
ot
N
ey
’re
en
o
th
e
S
sa
m
e
ta
n
0%
Th
R
0 of 20
on
0%
Work Review
 Tommy
lifts up a 10kg crate with constant
speed 2 m from the floor. He then holds
the crate at that height as he walks 20 m
down the hall. He then sets the crate down
with a constant speed onto a 1m tall table.
What is the total work done onto
the crate by Tommy?
29%
14%
J
00
23
0J
0%
20
4.
0J
3.
57%
10
2.
0J
100J
200J
2300J
0J
1.
What is the total work done onto
the crate by gravity?
14%
-2
00
J
0%
00
J
0%
-1
4.
0J
3.
86%
10
2.
0J
100J
-100J
-200J
0J
1.
What is the total work done onto
the crate?
0J
0%
20
0%
00
J
0%
-1
4.
0J
3.
100%
10
2.
0J
100J
-100J
200J
0J
1.
Work Review

Joey pulls a 15 kg sled across a snowy
field with a rope. The force of friction
acting on the sled is 10 N. The sled
accelerates across the field at a rate of 2
m/s2. If the sled is pulled a distance of
30m…(hint, find the applied force by
Joey before going on)
How much work is done on the sled
by Joey?
14%
J
00
45
00
J
0%
12
0%
0J
4.
90
3.
86%
0J
2.
300J
900J
1200J
4500J
30
1.
How much work is done on the sled
by friction?
-1
00
12
0%
20
0J
0%
J
0%
0J
4.
30
3.
100%
00
J
2.
-300J
300J
1200J
-1200J
-3
1.
What is the total work done onto
the sled ?
00
J
0%
12
0%
0J
0%
90
4.
0J
3.
100%
00
J
2.
-300J
0J
900J
1200J
-3
1.
 Grimmy
Work Review 2
pushes Granny in her wheelchair
up a 20m long ramp that has an incline of
30°. Granny has a mass of 50kg.
 What is the ideal force Grimmy has to
push?
 If
he actually has to push with a force of
300, what is the efficiency of the ramp?
Traffic Ticket

You are driving your car uphill along a straight road.
Suddenly, you see a car run a red light and enter the
intersection just ahead of you. You slam on your brakes
and skid in a straight line to a stop, leaving skid marks
100 feet long. A policeman observes the whole incident
and gives a ticket to the other car for running a red light.
He also gives you a ticket for exceeding the speed limit
of 30 mph. When you get home, you read your physics
book and estimate that the coefficient of kinetic friction
between your tires and the road was 0.60, and the
coefficient of static friction was 0.80. You estimate that
the hill made an angle of about 10owith the horizontal.
You look in your owner's manual and find that your car
weighs 2,050 lbs. Will you fight the traffic ticket in court?
Lesson #62
Topic: Conservation of Energy
Objectives: (After this class I will be able to)
1.
3/26/07
Describe how the total energy of a
system is conserved.
Warm Up: A 1kg stone is released from rest from the top of a 45m tall
cliff. What is the total energy of the stone before it is released? 1 sec after
release? 2 seconds after release? 3 seconds after release?
Assignment: Concept Development 8-1 due Wednesday.
A 1kg stone is released from rest from
the top of a 45m tall cliff. What is the
total energy of the stone before it is
released?
0%
0%
0J
45
J
0 of 20
0%
45
0%
0N
4.
45
3.
N
2.
45J
10N
450N
450J
10
1.
After falling for 1 second, what type
of energy does the stone have?
0%
es
e
se
tic
0%
in
e
th
of
ei
th
er
N
0 of 20
0%
K
Po
te
n
tia
l
0%
th
e
4.
of
3.
ot
h
2.
Potential
Kinetic
Both of these
Neither of these
B
1.
After falling for 1 second, what is the
height of the stone above the bottom of
the cliff?
m
0%
10
0 of 20
5m
0%
0%
0%
m
4.
40
3.
m
2.
5m
10m
35m
40m
35
1.
After falling for 1 second, what is the
potential energy of the stone?
0%
0%
0J
45
J
0 of 20
0%
45
0%
0J
4.
40
3.
J
2.
45J
50J
400J
450J
50
1.
After falling for 1 second, what is the
velocity of the stone?
m
/s
0%
10
5m
0 of 20
/s
0%
0%
0%
0m
/s
4.
80
3.
m
/s
2.
5m/s
10m/s
28m/s
800m/s
28
1.
After falling for 1 second, what is the
kinetic energy of the stone?
0%
0%
0J
10
J
0 of 20
0%
45
0%
0J
4.
40
3.
J
2.
10J
50J
400J
450J
50
1.
Conservation of Energy





The total energy of the stone at any given
moment is its potential energy plus its kinetic
energy.
Total Energy = PE + KE
The total energy of the stone is the same at
any time along the stone’s path as it falls.
The energy just transfers from all potential
energy (at the top) to all kinetic energy (at the
bottom).
When the object makes contact with the
ground, the energy is transferred again into
several other sources (heat, sound, bouncing).
Conservation of energy example

Observe a pendulum and describe the
conservation of energy throughout the
motion of the pendulum bob.
E
A
D
B
C
At what position(s) is the energy of
the pendulum only potential energy?
A&E
A only
C only
B&D
A,B,D,& E
,&
,B
A
A
0%
E
0%
D
ly
on
&
A
0%
,D
0%
E
0%
&
5.
B
4.
ly
3.
on
2.
C
1.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
At what position(s) is the energy of
the pendulum only kinetic energy?
A&E
A only
C only
B&D
A,B,D,& E
,&
,B
A
A
0%
E
0%
D
ly
on
&
A
0%
,D
0%
E
0%
&
5.
B
4.
ly
3.
on
2.
C
1.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
At what position(s) is the energy of
the pendulum both kinetic and
potential?
A&E
A only
C only
B&D
A,B,D,& E
3
4
5
6
7
8
9
10
11
12
14
15
,&
D
E
0%
,B
A
13
0%
16
17
18
A
2
ly
on
&
A
1
0%
,D
0%
E
0%
&
5.
B
4.
ly
3.
on
2.
C
1.
19
20
At what position(s) does the
pendulum have no kinetic energy?
A&E
A only
C only
B&D
A,B,D,& E
3
4
5
6
7
8
9
10
11
12
14
15
,&
D
E
0%
,B
A
13
0%
16
17
18
A
2
ly
on
&
A
1
0%
,D
0%
E
0%
&
5.
B
4.
ly
3.
on
2.
C
1.
19
20
Which path will cause the ball to go
the highest on the ramp?
Th
0 of 20
er
e
is
no
di
ffe
re
n
1
5.
ce
4.
4
3.
20% 20% 20% 20% 20%
3
2.
1
2
3
4
There is no
difference
2
1.
Solving problems using the
conservation of energy



Because energy is conserved, the total
energy of an object at an initial position is
equal to the total energy at any other
position.
KEi+PEi=KEf+PEf
½mvi2+mghi= ½mvf2+mghf
During a hurricane, a large tree limb, with a mass
of 22kg and a height of 13.3m above the ground,
falls on a roof that is 6m above the ground.
What is the kinetic energy of the limb when it hits
the roof?
1.
2.
3.
4.
2926J
1606J
1320J
12.08m/s
0%
2
0 of 20
6
92
0%
J
1
6
60
0%
J
1
0
32
0%
J
12
.
m
08
/s
During a hurricane, a large tree limb, with a mass
of 22kg and a height of 13.3m above the ground,
falls on a roof that is 6m above the ground.
What is the speed of the branch when it hits the
roof?
1.
2.
3.
4.
16m/s
1606m/s
11m/s
12m/s
0%
0 of 20
/s
m
6
1
0%
16
/s
m
6
0
0%
/s
m
1
1
0%
/s
m
2
1
A bike rider approaches a hill at a speed of 8.5m/s.
The combined mass of the bike and the rider is
85kg. The rider coasts up the hill. At what height
will the bike come to rest?
0%
m
0%
85
0%
5m
3.
0 of 20
6m
0%
0.
4.
5m
3.
2.
2.
3.6m
5m
722.5m
0.85m
72
1.
Suppose that the bike rider pedaled up the hill and
comes to a stop at the top. The height of the hill is
6m. How much work did the rider have to do to get
to the top of the hill?
0%
4m
0%
J
70
30
40
20
0 of 20
0%
J
0%
2.
4.
J
3.
00
2.
2040J
3070J
5100J
2.4m
51
1.
A skier starts from rest at the top of a 45m high hill,
skis down a 30° incline into a valley, and continues
up a 40m high hill. How fast is the skier moving at
the bottom of the valley?
0m
/s
0%
90
45
0 of 20
0m
/s
0%
0%
0%
5m
/s
4.
4.
3.
m
/s
2.
450m/s
900m/s
30m/s
4.5m/s
30
1.
A skier starts from rest at the top of a 45m high hill,
skis down a 30° incline into a valley, and continues
up a 40m high hill. How fast is the skier moving at
the top of the second hill?
m
/s
0%
30
10
0 of 20
m
/s
0%
0%
0%
m
/s
4.
20
3.
m
/s
2.
10m/s
30m/s
40m/s
20m/s
40
1.
Advanced problem

In a belly flop diving contest, the winner is
the diver who makes the biggest splash.
The splash is dependent not only on style,
but also on how much kinetic energy the
diver has on impact. Consider a contest in
which each contestant jumps from a 3m
high diving board. One diver has a mass of
136kg and simply steps off the platform.
Another diver has a mass of 102kg and
leaps upward from the platform. How high
would the second diver have to leap to
make a competitive splash?
Project
A
ball is launched vertically into the air
with an initial speed of _______ how high
did the ball go?
Winter Olympics

You have landed a summer job with a company that has been given
the contract to design the ski jump for the next Winter Olympics. The
track is coated with snow and has an angle of 25o from the
horizontal. A skier zips down the ski jump ramp so that he leaves it
at high speed. The winner is the person who jumps the farthest after
leaving the end of the ramp. Your task is to determine the height of
the starting gate above the end of the ramp, which will determine the
mechanical structure of the ski jump facility. You have been told that
the typical ski-jumper pushes off from the starting gate at a speed of
2.0 m/s. For safety reasons, your design should be such that for a
perfect run down the ramp, the skier's speed before leaving the end
of the ramp and sailing through the air should be no more than 80
km/hr. You run some experiments on various skies used by the
jumpers and determine that the coefficient of static friction between
the snow and the skis is 0.10 and its coefficient of kinetic friction is
0.02. Since the ski-jumpers bend over and wear very aerodynamic
suits, you decide to neglect the air resistance to make your design.
Lesson #63
Topic: Lab: Conservation of Energy
Objectives:
1.
3/28/07
(After this class I will be able to)
Use the conservation of energy to calculate
the velocity of a steel ball.
Warm Up: A ball rolls off of a 1m tall desk with an initial horizontal velocity of
1.5m/s. How far from the desk does the ball hit the ground?
Assignment: Calculate the velocity of the ball when it leaves
the desk and place the target at the appropriate spot on the
floor to have the ball land on the bull’s eye.
A ball rolls off of a 1m tall desk with an initial
horizontal velocity of 1.5m/s. How far from
the desk does the ball hit the ground?
1.
2.
3.
4.
.447m
.671m
1m
1.5m
20
5m
0%
1.
0%
1m
71
.6
47
.4
0
m
0%
m
0%