1. Good Afternoon!
Today we will:
review what we learned last week
write a short constructed response
take notes and solve some energy problems
Please do before the tardy bell:
find a calculator
look over your notes from Thursday – pay
special attention to the relationship between:
work done & kinetic energy
stopping distance and force of impact
2. Warm-Up
You’ve had five minutes to look
over your notes – now it’s time to
review
Get out a single sheet of paper and
number to five.
3. Warm-Up Quiz
1. If a chair at rest has work done
on it that results in the chair having
650 J of kinetic energy, how much
work was done?
4. Warm-Up Quiz
2. If a bowling ball had 1000 J of
energy as it entered the ball
delivery chute, and 200 J of energy
as it leaves the delivery chute, how
much work was done?
5. Warm-Up Quiz
3. A box is pushed across the floor,
giving it a kinetic energy of 800 J. If
the force applied was 200 N, how
far did the box travel?
6. How does cushioning decrease the
severity of the damage of a car crash?
Proficient answers will include:
1. The relationship between kinetic energy and
work done
2. the relationship between the impact force
and the stopping distance
3. scientific language
Advanced answers will include:
All of the above PLUS your own math
examples
7. Speed and Kinetic Energy
KE = ½ mv2
To safely stop a car traveling 9 m/s
(~ 20 mi/h), you will need about 6m
of stopping distance.
If you triple the speed (27 m/s or
60 mi/h), what would your
stopping distance be?
8. Speed and Kinetic Energy
KE = ½ mv2
If you triple your speed, you
increase your KE 9x’s.
Why?
9. Mass and Kinetic Energy
Which requires more force to stop
in 12 m, a 1000 kg passenger car
moving at 8 m/s or a 2000 kg utility
vehicle moving at 6m/s?
10. Kinetic Energy and
Damage
Remember:
The total amount of kinetic energy is
the total amount of work that can be
done
In terms of a car crash, “work done”
is the damage
11. Kinetic Energy Problem #1
a 70.0 kg person is traveling in a
car going 13 m/s (~ 29 mi/h).
What is the person’s kinetic
energy?
12. Kinetic Energy Problem #1
To stop the person, something has to do
5915 J of work
you might round 5915 J to 5900 to account
for the two significant digits
If the thing that does the work is the
windshield (how many of you don’t wear
a seat belt because “you’re just going up
the street?”), the stopping distance
would be about 3.0 cm (0.030 m).
How much force would be applied to the
person’s skull?
13. Kinetic Energy Problem #1
If instead of the windshield, the
person’s air bag did the work, what
would the force on the person’s
skull be? (air bags would increase
the stopping distance from 0.03 m
to 0.3 m)
14. Kinetic Energy and Car
Crashes
That’s still a lot of force, but it’s
10x’s less than the windshield.
Luckily, cars are equipped with
other devices designed to absorb
the kinetic energy.
seat belts
crumple zones
15. Kinetic Energy Problem #2
A total of 12,000 J of work is required to
stop a 45 kg cart.
a) what speed was the cart traveling
before it was brought to a stop?
b) if the cart was stopped over a distance
of 3m, what was the magnitude of the
force?
16. Finish the Warm-Up Quiz
(Reg)
4. Two eggs are thrown with equal
velocity. Egg #1 has a stopping
distance of 0.5 meters and egg #2
has a stopping distance of 1.0
meters. Which egg has the
greatest force of impact?
17. Finish the Warm-Up Quiz
(Reg)
5. Jamie throws a baseball at a sheet
and the ball pushes the sheet back 0.3
meters.
Jordan throws a baseball at a sheet
and pushes it back 0.6 meters.
Compare the kinetic energy Jamie
gave the ball compared to the kinetic
energy Jordan gave the ball. Be as
specific as you can.
18. Finish the Warm-Up Quiz
(Hon)
4. An egg is given 100 J of kinetic
energy. It is brought to a stop over
a distance of 2 meters. If the
impact force that will crack an egg
is 60 N, does the egg shell break?
Use mathematical fact to support
your answer!
19. Finish the Warm-Up Quiz
(Hon)
5. A bowling ball has a mass of 7
kg. It is rolled down a frictionless
bowling lane at a velocity of 10 m/s.
It strikes one 2 kg bowling pin
head-on. If there is no back-stop,
how far will the pin travel? Use
mathematical fact to support your
answer!
20. Finish the Warm-Up Quiz
(Hon ADV)
6. A chicken egg has a mass of 60
grams (0.06 kg). If it is dropped
from a height of 0.8 m and creates
a 2.5 cm dent in the flour, how
much impact force was applied to
the egg? BE CAREFUL WITH YOUR
UNITS!!! Use mathematical fact to
support your answer!
