Hi folks,
Today our future physicists under took a little mechanical engineering task. I gave them the task to create the most energy efficient vehicle that they could. Using a variety of materials, they were to create a vehicle that uses as much of the energy they gave it as efficiently as possible. They had to measure the energy they put into the vehicle (primarily gravitational potential energy) and the energy out and figure out how energy efficient their vehicle was.
Homework for 3/3 is to do the enclosed questions. I've included the answers to the Olympic energy questions to help you study.
1. Thinking about the energy formulas, tell me if it make sense to have a heavy vehicle or a light vehicle as far as gPE goes.
2. If you created a balloon car, would you want it to be heavy? Why or why not?
3. If you and a friend were on identical sleds and your friend weighs twice as much as you do, which of you would go farther? Which of you would have more velocity? Describe this in relation to momentum and describe this in relation to energy.
Use these formulas to solve the following Olympic energy problems. Answers below.
gPE = MgH
KE = ½ MV^2 (^2 means squared)
W = FD
1. A ski jumper who has a mass of 70 kg stands at the top of a ski jump that is 20m tall.
a. What is his potential energy?
b. If there's no friction, what would his speed be as he launches from the jump?
c. If his speed is 14 m/s, what is the energy efficiency of the ramp?
d. What work did friction do on our ski hero?
e. What was the average force of friction between the ramp and his skis if he travels
75 m down the ramp
2. a. If the Jamaican bob sled with a mass of 300 kg reaches a top speed of 150 km/h (42 m/s), what was the least amount of energy the bob sled started with?
b. What was the lowest height the bob sled started at?
c. If the track is 2200m long, what work did friction do on our Jamaican bob sledders by the time the team comes to a complete rest at the bottom?
d. If the height of the track was really 200 m, what was the energy efficiency of the bob sled?
1. a. gPE = Mgh
70kg x 20 m x 10 m/s^2 = 14,000J
b. KE = ½ MV^2
14,000 J = ½ 70 kg x v^2
v = 20 m/s
c. KE = ½ 70kg x (14)^2
KE = 6860 J
Work out/ Work in x 100
6860/14000 x 100 = 49% Efficient
d. 14,000J - 6860J = 7140 J
e. W = FD
7140J = F x 75m
F = 95.2 N
2. a. KE = ½ MV^2
KE = ½ 300kg (42 m/s)^2
KE = 264,600 J
b. gPE = MgH
264,600 = 300kg x 10m/s^2 x H
H = 88.2 m
c. W = FD
264,600 J = F x 2200 m
F = 120.27 N
d. gPE = MgH
gPE = 300 kg x 10 m/s^2 x 200 m
gPE = 600,000 J That's the maximum amount of energy. Since their energy was 264,600 J their energy efficiency was…
Work out / Work in x 100
264,600/ 600,000 x 100 = 44%
Tuesday, February 25, 2014
Monday, February 24, 2014
Payment for Science Classes
Hi folks,
Just a reminder, that payment is due for the final session of classes. The cost is $250 for the full 2 hour class and $180 for the 1.5 hour class.
If you wish to mail your payments, my address is 3105 Whitfield Rd. Chapel Hill, NC 27514.
I hope everyone is enjoying this wonderful spring-like weather.
Jim Mueller
Just a reminder, that payment is due for the final session of classes. The cost is $250 for the full 2 hour class and $180 for the 1.5 hour class.
If you wish to mail your payments, my address is 3105 Whitfield Rd. Chapel Hill, NC 27514.
I hope everyone is enjoying this wonderful spring-like weather.
Jim Mueller
Tuesday, February 18, 2014
Recording of Physics week 21: Working with Energy Formulas
This is short since most of the class was lab work.
Your video is now on YouTube.
Physics week 21
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Monday, February 17, 2014
2/17 Physics update and homework due 2/24
Hi folks,
Today we began the next part of our energy unit with is energy in motion, in other words, waves. Today we worked on the concept of frequency and hertz.
In order to work with this, the students created 3 pendulums. One of which had a frequency of .5 Hz, one had a frequency of 1 Hz and the last had a frequency of 2 Hz. From their data, they then predicted what length of string would have a frequency of 1.5 Hz.
Extra Credit possibility. Continue working with pendulums and do a lab exploring one of the many variables you thought of today during class. For example, changing the weight of the bob. Does the height of the swing matter? Does interference of the swing matter.
Homework due 2/24
Read Conceptual Physics pgs 103-118
Do Review Questions pg 119 and 120 #'s 7-12, 18 and 20
Do Plug and Chug pg 120 #'s 4-7
Do Think and Explain pg 120 and 121 #'s 2 and 3.
Today we began the next part of our energy unit with is energy in motion, in other words, waves. Today we worked on the concept of frequency and hertz.
In order to work with this, the students created 3 pendulums. One of which had a frequency of .5 Hz, one had a frequency of 1 Hz and the last had a frequency of 2 Hz. From their data, they then predicted what length of string would have a frequency of 1.5 Hz.
Extra Credit possibility. Continue working with pendulums and do a lab exploring one of the many variables you thought of today during class. For example, changing the weight of the bob. Does the height of the swing matter? Does interference of the swing matter.
Homework due 2/24
Read Conceptual Physics pgs 103-118
Do Review Questions pg 119 and 120 #'s 7-12, 18 and 20
Do Plug and Chug pg 120 #'s 4-7
Do Think and Explain pg 120 and 121 #'s 2 and 3.
Wednesday, February 12, 2014
Monday, February 10, 2014
2/10 physics update and homework due 2/17
Hi Folks,
Today we got into the concept of Potential and Kinetic energy and how they change into each other. We also discussed energy efficiency and conservation of energy.
For homework this week:
Find the energy the ramp stole from the ball (if you haven't already finished that in class).
Find the energy efficiency of the ramp. Take the work out (the energy the box was hit with) divided by the work in (the potential energy the ball started with) and multiply that by 100 to convert it to a percentage.
Read the Potential and Kinetic Energy chapter in the eBook
Open the following simulation and use it to answer the following questions in the .pdf.
Tuesday, February 4, 2014
2-3 physics update and homework due 2/10
Hi folks,
Today we continued our investigation into simple machines and their relation to work. We did some work with pulleys and discovered the inverse relationship between distance and force.
For homework this week:
Read the pulley chapter in the book.
Take a look at the enclosed .pdf and do all the questions at the end.
Also, answer the following questions.
1. With the pulleys, how did work out relate to work in?
2. With the levers, did work out relate to work in? It should have. So what wasn't measured that caused work out to not relate to work in in the same way as the pulleys?
3. What relationship did force have in regards to distance as you worked with the pulleys?
4. As you increased the number of pulleys, what effect did that have on the effort force? What effect did it have on the effort distance?
5. a. If you were lifting a load that required a force of 10N with one pulley, what effort force would be required?
b. Same question, but now you're using 2 pulleys?
c. How about 10 pulleys?
6. a. If you were lifting that load 1 meter, what would the work in distance be for one pulley?
b. 2 pulleys?
c. 10 pulleys?
Today we continued our investigation into simple machines and their relation to work. We did some work with pulleys and discovered the inverse relationship between distance and force.
For homework this week:
Read the pulley chapter in the book.
Take a look at the enclosed .pdf and do all the questions at the end.
Also, answer the following questions.
1. With the pulleys, how did work out relate to work in?
2. With the levers, did work out relate to work in? It should have. So what wasn't measured that caused work out to not relate to work in in the same way as the pulleys?
3. What relationship did force have in regards to distance as you worked with the pulleys?
4. As you increased the number of pulleys, what effect did that have on the effort force? What effect did it have on the effort distance?
5. a. If you were lifting a load that required a force of 10N with one pulley, what effort force would be required?
b. Same question, but now you're using 2 pulleys?
c. How about 10 pulleys?
6. a. If you were lifting that load 1 meter, what would the work in distance be for one pulley?
b. 2 pulleys?
c. 10 pulleys?
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