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Feb. 21
Mega Review
Homework
1. Calculate the work done as a 100 N force pushes a crate 5 m along a
floor.
2. Calculate the work done by a person who carries a 50 N box
vertically 3m up a ladder.
3. What is the potential energy of the 50 N box when raised 3 m?
4. Calculate the power expended by the person who carries the 50 N
box 3 m high in 3 s.
5. Calculate the kinetic energy of a 10 kg cart traveling at 4 m/s.
6. Calculate the change in KE when the speed of a 10 kg cart increases
from 4 m/s to 10 m/s.
7. How much work is required to make the change in KE in the
previous problem?
HW Due
#6-13
Ch 8 Guided Notes
**Place both of these in In Box!**
Tonight’s
HW
Read & Study p. 670-672. On p. 672, complete
#1-7 ***WRITE the FULL Q&A. If you would rather print
the questions, they are typed on my website – you may
copy, paste, and print
Ch 8 test on March 3
Do Now
Take one
Read the 1st
column.
Complete
the 2nd
Do Now
Complete the 3rd column. You have all class to think
about your response for the last column – that will be
your exit for today (in addition to the back of this paper)
Goals for Today
1. Concept Development– take a packet and complete.
Check in at the stop signs.
***Not finished in class? Becomes HW!!! ***
2. Check your HW!!!
– In groups, review the notes from last class that were also
HW. Questions? Check with a teacher!
– Check the book HW (#1-13, 21-23) with your groups.
– Either today or next week, we will have time to clicker
review all the HW as a class. Need help? ASK!
3. You will get back your Disney Quiz. You will have time
to conference w/ teacher if you need help or
clarification!
4. Finished? Complete the ***Boxed Questions on last
class’ notes (all the questions before these were HW
due today check in at STOP SIGNS!) ***These are NOT
HW if not done in class  we will finish these next week in class
Take out your book HW
• #1-4
• #5, 21-23
• #6-13
1. What do we call the quantity force
times distance, and what quantity can
it change?
1.
2.
3.
4.
Work, energy
Power, work
Weight, energy
Momentum, work
25%
1
25%
25%
2
3
25%
4
2. Work is required to lift a barbell.
How many more times work is
required to life the same barbell 3
times as high?
1. Half as much
2. Twice as much
3. Three times as
much
4. Nine times as
much
93%
0%
1
7%
2
0%
3
4
3. Which requires more work: lifting a
10 kg load a vertical distance of 2m,
or lifting a 5kg load a vertical distance
of 4m?
A. lifting a 10 kg load
a vertical distance
of 2m
B. lifting a 5kg load a
vertical distance
of 4m
C. same work in
both cases
56%
31%
13%
A.
B.
C.
4. How much work is done on an
object when a force of 10N pushes it
a distance of 10m?
A.
B.
C.
D.
87%
1 Joule
1 Watt
100 Joules
100 Watts
13%
0%
A.
B.
0%
C.
D.
5a. How much power is required to
do 100J of work on an object in 1
second?
A.
B.
C.
D.
56%
1 Joule
1 Watt
100 Joules
100 Watts
31%
6%
A.
6%
B.
C.
D.
5b. How much power is required to
do 100J of work on an object in 0.5
second?
1.
2.
3.
4.
50 J
50 W
200 J
200 W
63%
26%
5%
1
5%
2
3
4
IMPORTANT!
• SAME work…
• HALF the time…
• TWICE the power!!!
Check Question!!!
Work and Power are __proportional
1. Directly
2. Inversely
3. I have no idea
33%
1
33%
2
33%
3
Check Question!!!
Time and Power are ___ proportional
1. Directly
2. Inversely
3. I have no idea
33%
1
33%
2
33%
3
POPCORN!
6. What are the 2 main forms of Mechanical
Energy?
(1 person will give one, and a 2nd person will give
the other)
7a. If you do 100 J of work to elevate
a bucket of water, what is its grav. PE
relative to its starting point?
1.
2.
3.
4.
More than 100 J
Less than 100 J
100 J
Zero
25%
1
25%
25%
2
3
25%
4
7b. If you lift it 2x as high, what’s
its PE?
1. Less than 100 J
2. 100 J
3. More than 100 J, but
less than 200 J
4. 200 J
5. More than 200 J
6. Zero
17%
1
17%
2
17%
17%
3
4
17%
5
17%
6
Check Question!!!
Grav. PE and Height are ___ proportional
1. Directly
2. Inversely
3. I have no idea
33%
1
33%
2
33%
3
8. A boulder is raised above the
ground so that its grav. PE is 200 J
(relative to the ground). Then it’s
dropped. What’s its KE the INSTANT
just before hitting the ground?
25%
1.
2.
3.
4.
25%
25%
2
3
25%
More than 200 J
Less than 200 J
200 J
Zero
1
4
9a. Suppose an automobile has 2000 J
of kinetic energy. When it moves a
twice the speed, what will be its
kinetic energy?
25%
1.
2.
3.
4.
5.
6.
The same (2000 J)
2x as much (4000 J)
3x as much (6000 J)
4 as much (8000 J)
6x as much (12,000 J)
9x as much (18,000 J)
1
25%
25%
2
3
25%
4
9b. Suppose an automobile has 2000 J
of kinetic energy. What’s its kinetic
energy at three times the speed?
25%
1.
2.
3.
4.
5.
6.
The same (2000 J)
2x as much (4000 J)
3x as much (6000 J)
4 as much (8000 J)
6x as much (12,000 J)
9x as much (18,000 J)
1
25%
25%
2
3
25%
4
KE
is directly proportional
to the SQUARE
of the velocity!
10. What will be the kinetic energy of
an arrow having a potential energy of
50 J after it is shot from a bow?
25%
25%
25%
2
3
25%
1. The same (50 J)
2. More than 50 J
3. Less than 50 J
1
4
POPCORN
11. What does it mean to say that in any
system the total energy score stays the
same?
POPCORN
11. What does it mean to say that in any
system the total energy score stays the
same?
Energy is conserved.
POPCORN
12. In what sense is energy from coal actually
solar energy?
POPCORN
12. In what sense is energy from coal actually
solar energy?
Coal is formed from organic material. Organic
materials (plants, the animals that eat plants,
and the animals that eat animals that eat
plants) get their energy from the sun.
POPCORN
13. How does the amount of work done on an
automobile by its engine relate to the energy
content of the gasoline?
POPCORN
13. How does the amount of work done on an
automobile by its engine relate to the energy
content of the gasoline?
It is less than the energy contained in the gasoline.
An automobile engine is not 100% efficient.
(Some of the gas energy powers the car…but some
is transferred into heat, sound, etc… TOTAL
ENERGY stays the same, but that sum is made of
diff. types of energy!)
CHECK QUESTIONS!
Can energy ever be created?
100%
1. Yes
2. No
3. Sometimes
0%
1
0%
2
3
Can energy ever be destroyed?
89%
1. Yes
2. No
3. Sometimes
11%
0%
1
2
3
Does an object with momentum
always have energy?
1. Yes
2. No
59%
41%
1
2
Does an object with energy always
have momentum?
1. Yes
2. No
67%
33%
0%
1
2
3
If a mouse and an elephant both run
with the same kinetic energy, can you
say which is running faster?
60%
1. The mouse
2. the elephant
3. Not enough info
to say
25%
15%
1
2
3
Using the diagram below… what
happens to the skater’s KE as he goes
DOWN the ramp?
1. Increases
2. Decreases
3. Stays the same
33%
1
33%
2
33%
3
Using the diagram below… what
happens to the skater’s KE as he goes
UP the ramp?
1. Increases
2. Decreases
3. Stays the same
33%
1
33%
2
33%
3
Using the diagram below… what
happens to the skater’s PE as he goes
DOWN the ramp?
1. Increases
2. Decreases
3. Stays the same
33%
1
33%
2
33%
3
Using the diagram below… what
happens to the skater’s PE as he goes
UP the ramp?
1. Increases
2. Decreases
3. Stays the same
33%
1
33%
2
33%
3
Using the diagram below… what
happens to the skater’s TOTAL
ENERGY as he goes UP the ramp?
1. Increases
2. Decreases
3. Stays the same
33%
1
33%
2
33%
3
Using the diagram below… what
happens to the skater’s TOTAL
ENERGY as he goes DOWN the ramp?
1. Increases
2. Decreases
3. Stays the same
33%
1
33%
2
33%
3