2/25 update and homework due 3/4

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 3/4 is to do the enclosed questions.

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%

Recording for 2/25 Physics Class - Calories and Joules

http://youtu.be/CvhyAUcV1VM

Physics Class is ON for today

Hi folks,

From what I'm hearing and seeing it looks like the roads are in decent shape so I'm going to hold class today. Be safe and we'll see you all soon.

Jim Mueller

Physics Class Today

Hi folks,

The roads are fine by me but I want to check in and see how things are by you all. I'm planning on holding class today but let me know if you can't make it in. If too many folks can't make it we may need to cancel class again.

Jim Mueller

No Physics Class Today!

Hi folks,

From the reports I'm getting in, it looks like quite a few folks are still stranded by their driveways.

Let's skip class for this week.

Be safe and warm everyone.

Jim Mueller

Physics Class Today?

Hi folks,

So, how are things looking? New on the "things to think about" is that it may snow today starting around 4:00. Looks like that should be a light dusting, however, with accumulation less then half of an inch.

Let me know how you feel about getting to class and I'll make a decision around 12:00 at the latest.

Jim Mueller

Physics class and the weather

Hi folks,

I'm seeing reports that quite a few schools are planning on being closed due to road conditions tomorrow.  What I would like to do is email everyone around 10:00 tomorrow and see how you all feel about driving to class.  Hopefully a miracle will happen and the roads will be clear and safe.

In the meantime, have a warm and safe night everyone.

Never Stop Wondering

"Science Jim"  Mueller

(919) 907-3217

A Fun Approach to Serious Physics!

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Physics Update 2/11 and homework due 2/18

Hi folks,

Today we got a bit more specific about energy and talked about potential energy, kinetic energy and conservation of energy.  

For homework this week I want you to answer the following questions.  Good luck!

Assume the following to answer the questions below:

Mass of ball = .05 kg

Velocity of ball on ramp = .4 m/s

Time on ramp = .3 s

Time to stop rolling after getting off ramp 3 s

Distance ball rolled after getting off ramp = 3 m

What makes the ball stop after getting off the ramp?

What was the velocity of the ball after getting off the ramp?

What was the gPE of the ball at the top of the ramp?

What was the gPE of the ball at the bottom of the ramp?

What happened to the gPE?

What was the KE of the ball at the bottom of the ramp?

Where did the energy of the system originally come from?

What amount of work did friction do to the ball after it got off the ramp to the point where the ball stopped rolling?

Where did the energy go that caused the ball to stop?

What is the friction force of the carpet?

Recording for 2/11 Physics Class - Potential and Kinetic Energy

http://youtu.be/odZraZiFhZk

2/4 Physics update and homework due 2/11

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?