Download Energy Module 1H - Tamalpais Union High School District

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LABETTE
A CALCULATION OF PERSONAL POWER
INTRODUCTION
My dad gave me a car three days after I turned
sixteen. I was ecstatic. I couldn’t contain myself. My
very own car – I couldn’t believe it. And even though
he towed it home, it was the most beautiful two tons
of metal I think I had ever seen. He said if I could get
it to run, it was mine. The ‘62 Pontiac Grand Prix had
almost 100,000 miles and an engine that had died, but
after I got it to run I was amazed at its incredible
power – 303 horsepower. No sixteen-year-old boy
should be allowed to tame that much power. Oh, the
stories I could tell. You might wonder how much 303
horsepower really is and how it compares to your
own personal power. It’s a lot by today’s automotive
standards. A standard mid-size American car
probably has around half the power of my old Grand
Prix (and probably gets three times the mileage).
How it compares to your own personal power is an
interesting question. I’ll have you do three
experiments to determine your personal power: one
in which you do work with your biceps (curling a
dumbbell), one in which you do work with your
triceps (doing pushups), and one in which you do
work with your legs (climbing stairs). It seems that
determining personal power using this last method is
somewhat of a tradition at Tam. I ran across an old
article from the Tam News a few years ago when I
was moving some furniture in my classroom. It was
an article from the March 8, 1940 issue, written about
the annual personal power competition in physics.
The way the students measured their power was to
time themselves running up a set of stairs as quickly
as possible. Moving up the stairs caused them to
change their gravitational potential energy and
running increased the rate of that energy change.
We’ll do the same thing, using the stairs outside the
physics classroom. Students always ask if they can
skip steps. The answer is yes, because all you’re
trying to do is increase your distance above the Earth
as quickly as possible. The method doesn’t matter.
Students also usually wonder if they can get a
running start. I think this is fine. In fact, you want
your speed at the bottom to be the same as your speed
at the top so that there is no change in your kinetic
energy, only your potential energy. So, on your
marks, get set, GO! The school record for boys is
2.16 hp by Elmo Maggiora (class of 1938) and for
girls it’s 1.41 hp by Helen Wendering (class of 1933).
PURPOSE
To calculate your own personal power.
PROCEDURE (PART 1 - BICEPS)
1.
Record the weight of the dumbbell you will use.
2.
Record the vertical distance the dumbbell moves as you curl it.
(Make sure you don’t move your shoulder – only your elbow).
3.
Record the number of curls you can do in 30 seconds.
DATA (PART 1 - BICEPS)
1.
Weight of dumbbell in pounds: ___________
2.
Weight in Newtons: ___________
(1 pound = 4.45 N)
3.
Vertical distance of curl: ___________
4.
Number of curls in 30 s: ___________
Figure 13.5: Alex MacDonald, Class
of 2004
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QUESTIONS/CALCULATIONS (PART 1 - BICEPS) SHOW ALL WORK
1.
Calculate the total work done in 30 seconds of curling.
2.
Calculate your personal power using biceps and express it in both watts and in horsepower.
(1 horsepower = 746 watts)
PROCEDURE (PART 2 – BACK AND TRICEPS)
1.
With either your knees or toes on a scale, place yourself in
the up part of the pushup position. Then do the same thing
except put yourself in the down part of the pushup
position. Average these two measurements and subtract
this weight from your body weight. Record this difference
as the weight you will be lifting during the pushup.
2.
Record the vertical distance your shoulders rise as you do
a pushup.
3.
Record the number of full pushups (all the way down) you
can do in 30 seconds.
DATA (PART 2 - TRICEPS)
Figure 13.6: Eric Andrews, Class of 2009
1.
Weight lifted during pushup (lbs): ___________
3.
Vertical distance of pushup: ___________
2.
Weight lifted during pushup (N): ___________
4.
Number of pushups in 30 s: ___________
QUESTIONS/CALCULATIONS (PART 2 – BACK AND TRICEPS) SHOW ALL WORK
1.
Calculate the total work done in 30 seconds of pushups.
2.
Calculate your personal power using triceps and express it in both watts and in horsepower.
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PROCEDURE (PART 3 - LEGS)
1.
Record your weight
2.
Measure the height of a stair outside the back door of the
physics classroom.
3.
Have your partner use a stopwatch to measure the time
required for you to run at full speed up the flight of
stairs outside the back door of the physics classroom. In
order for the transferred energy to be exclusively
gravitational potential energy, you should be moving at
the same speed when you cross the top stair as you are
moving when you start at the bottom stair (not stopped
and not sprinting). So approach the bottom step at a fast
walk and then go to full speed as soon as you reach the
first step.
DATA (PART 3 - LEGS)
1.
Weight in pounds:
___________
2.
Weight in Newtons: ___________
3.
Height of step:
4.
Total height climbed:
___________
___________
Figure 13.7: Beth Behrs, Class of 2004
5.
Time to climb stairs:
___________
QUESTIONS/CALCULATIONS (PART 3 - LEGS) SHOW ALL WORK
1.
Calculate the total work done in climbing the stairs.
2.
Calculate your personal power using legs and express it in both watts and in horsepower.
3.
Determine the following ratios (rounded to the nearest integer) of power:
TRICEP TO BICEP
LEG TO TRICEP
LEG TO BICEP
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100% CORRECT
For each of the following questions, give clear and complete evidence for your choice in the space provided.
1. _____
When a force is applied, work
a. must always be done
b. may be done
c. is never done
2. _____
A box weighs 50 N and moves at constant speed across a horizontal frictionless surface. How much work is done
on the box over the distance of 4.0 meters?
a. 0 J
b. 200 J
c. 1960 J
3. _____
A 50-N object was lifted 2.0 m vertically and is being held there. How much work is being done in holding the
box in this position?
a. more than 100 J
b. 100 J
c. less than 100 J, but more than 0 J
d. 0
4. _____
Average walking speed is about 2 m/s. A sprinter can reach 8 m/s. How much more kinetic energy does a
person’s body have when sprinting compared to walking?
a. two times more
b. four times more
c. eight times more
d. 16 times more
5. _____
A person lifts a 10 kg block to a table top in 2.0 seconds. He lifts an identical block a second time in 1.5 seconds.
What is true about his work and power during the lifting of the second block?
a. work same, power same
b. work more, power same
c. work same, power more
d. work more, power more
6. _____
A 50-kg physics student climbs a flight of stairs in 7.5 seconds. Each of the 60 steps is 20-cm high. What is her
power?
a. 80 W
b. 133 W
c. 600 W
d. 784 W
e. 8000 W
7. _____
A 9000-W motor lifts a 4500-kg elevator to a height of 12 m. How long does it take to do this?
a. 6.0 s
b. 24 s
c. 38 s
d. 59 s
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QUESTIONS AND PROBLEMS
WORK AND POWER
Do the following questions and problems from the Giancoli book in the space provided below.
Pages 160 – 164 Question 2; Problems 3, 5, 10, 58, 64, 66, 87
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100% CORRECT
LABETTE
THE PHYSICS OF SIMPLE MACHINES
PURPOSE
To build a simple machine and to analyze its physical features.
PROCEDURE
1.
2.
3.
4.
Build a simple pulley system as illustrated in class.
Use a spring scale to measure the weight that will be lifted (using all the weights provided).
Use a spring scale to measure the force required to lift the weight using the pulley system. (You must be moving
the pulley system when you make this measurement.)
Measure the distance you must pull on the pulley system in order to lift the weight 0.10 m. (Round this to the
nearest integer multiple of 0.10 m.)
DATA
Resistance Force: ___________
Effort Force: ___________
Resistance Distance: ___________
Effort Distance: ___________
QUESTIONS/CALCULATIONS SHOW ALL WORK
1.
Calculate the work input.
2.
Calculate the work output.
3.
Calculate the actual mechanical advantage.
4.
Calculate the ideal mechanical advantage.
5.
Calculate the efficiency of the machine.
6.
Calculate the amount of heat produced?
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7.
Give some rationale for the reason why this machine
should have the ideal mechanical advantage that it
has. (Hint: This is not about comparing effort and
resistance distances. It’s about looking at the number
of supporting strings.)
8.
Let’s say that instead of using two double pulleys,
you used two triple pulleys. Assume the friction per
individual pulley wheel is the same as before. Show
careful calculations for the new effort force?
QUESTIONS AND PROBLEMS
SIMPLE MACHINES
1.
A pulley system lifts a 1345-N weight a distance of 0.975 m. A 375-N force is exerted through a distance of
3.90 m.
a. If the machine were ideal, how much force would have needed to be applied to lift the 1345 N weight?
b. What is the efficiency of the system?
c. How much heat is produced?
d. How much force would need to be applied to this actual pulley system in order to lift a 2000 N weight?
2.
A 1000-N piano is raised a distance of 5.00 m using a set of pulleys. It requires pulling 20.0 m of rope.
a. How much effort force would need to be applied if this were an ideal machine?
b. If the machine were 75% efficient, how much effort force would be used?
c. What is the ideal mechanical advantage and the actual mechanical advantage?
3.
An inclined plane is 18 m long and reaches a height of 4.5 m high.
a. What force parallel to the ramp is required to slide a 25-kg box to the top of the ramp if friction is
neglected?
b. What is the IMA of the ramp?
c. What is the AMA if it actually requires a parallel force of 75 N to push the box?
d. What is the efficiency of the machine in this case?
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4.
A 10-m long inclined plane, whose maximum height is 2.0 m has an efficiency of 70%.
a. How much force must be applied to a 50-kg box to move it along the plane?
b. What is the actual mechanical advantage of the inclined plane?
c. How much heat is produced in moving the block up the plane?
d. How much force would have to be applied if the plane were an ideal simple machine?
5.
A ramp is used to move a refrigerator into the back of a truck. The refrigerator has a weight of 1127 N. The
ramp is 2.10 m long and rises 0.850 m off the ground. The mover pulls the dolly with a force of 496 N up
the ramp. What is the efficiency of the machine?
6.
A pulley system has an efficiency of 70%. When a student uses it to lift an engine out of a car, she pulls 10
m for every 1-m that the engine is lifted. How much force does she have to apply in order to lift the 2000-N
engine?
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Move ahead
100% CORRECT
For each of the following questions, give clear and complete evidence for your choice in the space
provided.
1. _____
Two cars, with the same mass, but initially at different altitudes, both increase their altitude by 1,000 m. Which
one (if either) has the greater increase in gravitational potential energy?
a. the lower altitude car
b. the higher altitude car
c. both the same
2. _____
2.0 J of energy are used to stretch a rubber band 3.0 cm. If 4.0 J of energy were used to stretch the same
rubber band, how much would the stretch increase to?
a. less than 6.0 cm
b. 6.0 cm
c. more than 6.0 cm, but less than 12 cm
d. 12 cm
3. _____
If a pole-vaulter were somehow able to increase his fastest running speed to double, how much higher
should he be able to vault himself?
a. less than twice as high
b. twice as high
c. more than twice as high
4. _____
If a person using a slingshot stretched the elastic twice as far and then shot a rock, how much faster would
the rock leave the slingshot?
a. less than twice as fast
b. twice as fast
c. more than twice as fast
5. _____
If a person using a slingshot stretched the elastic twice as far and then shot a rock straight up, how much
higher would the rock go?
a. less than twice as high
b. twice as high
c. more than twice as high
6. _____
A person on the edge of a roof throws a ball downward. It strikes the ground with 100 J of kinetic energy.
The person throws another identical ball upward with the same initial speed, and this too falls to the
ground. Neglecting air resistance, the second ball hits the ground with a kinetic energy of
a. 100 J
b. 200 J
c. less than 100 J
d. more than 200 J
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QUESTIONS AND PROBLEMS
CONSERVATION OF ENERGY
Do the following questions and problems from the Giancoli book in the space provided on the next two pages.
Pages 160 – 166 Question 10, 11, 19; Problems 37, 39, 42, 49, 52, 54, 55, 76
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