1. Energy & Thermodynamics
Chapter 10 review
Energy & Thermodynamics

2. 1 question
1 thing you learned or could take away
Per group
**if you do not ask a question I will on students to ask, so be prepared!

3. Test next Class – Monday. Vocab and equation chart due Monday
Test next Class – Monday! Vocab and equation chart due Monday! Study review on google drive! (link on the front whiteboard)

4. – some letters used more than once.
Energy stored in the bonds of atoms.
The ability to do work.
Energy due to position or motion.
Heat energy – also caused by friction.
States that energy can only be converted to one form or another.
Light – electromagnetic.
Rate at which energy is converted from one form to another.
States that output work is always less than the amount of heat that flows.
The total matter and energy stays the same.
Describes how well energy is converted from one form to another.
Movement of electrons.
Equal to work divided by time.
Joule/Second
1) Energy 2) Power 3)Mechanical Energy 4)Chemical Energy 5) 2nd Law of thermodynamics 6) Steady state 7) 1st law of thermodynamics 8)Efficiency 9)Radiant Energy 10) Thermal Energy 11) Electrical Energy 12) 1 Watt
Match the following
– some letters used more than once.

5. Answers: B
G,L C A H I E J F D K M

6. Calculate the Efficiency of the machine that Needs 100 Joules of work input and yields an output of 34 joules. Is it very efficient?
Efficiency = (work output/ work input) x 100 =34% , Not very efficient

7. a machine that needs 100,000 J of work has an efficiency of 90%
a machine that needs 100,000 J of work has an efficiency of 90%. Calculate the work output of the machine.
Work output = Efficiency x Work Input = 90,000 J

8. The roller coaster ride is 50 meters tall and reaches a speed of 20 m/s at the bottom. How efficient is the ride? (HINT – you can use any mass you want b/c it will cancel)
Efficiency = ke/pe x 100 Or
Efficiency = ½ mv2 x 100
mgh
Efficiency = 40.8%

9. a roller coaster goes 50 m/s at the bottom of the first hill
a roller coaster goes 50 m/s at the bottom of the first hill. You estimate the efficiency of the tracks and cars you are using is 80%. How high must the first hill be?
Ek = 1/2mv2
Ep = mgh
Efficiency = Wo/Wi
Given:
v= 50 m/s
Efficiency = .80
First find work output by solving for Kinetic Energy.
Ek = 1/2mv2
Ek = 1/2m (50)2
Ek = 1250 J
Then solve for work input using Efficiency Equation.
Work input = Work output/Efficiency
Wi = 1250 / .8
= J
Then solve for height using the Potential Energy Equation.
Ep = mgh so h=Ep/(mg)
h = / (9.8)
h = 159 m
Assume m=1kg

10. Calculate the power of the machine that does 500 J of work in 5 seconds.
P = work / time = 500J / 5s = 100 W

11. How much energy is needed to power a 75-W light bulb for 3 seconds?
Power = Work/time Work = Power x time =75 x 3 = 225 J

12. You exert a vertical force of 60 N to lift a box a distance of 1 meter over a 2 second period. How much power did you use?
P=W/T
W=FxD
W = 60N x 1m = 60J
P = 60J / 2s = 30W

13. After a large snowstorm, you shovel 2,000 kg of snow off your sidewalk in 3600 seconds. You lift the shovel to an average height of 1.2 meters while you’re piling the snow in your yard. a) What was your power in watts and horsepower?
F=mg
F=(2000kg)(9.8)
F=19,600 N
W=Fd
W=(19,600 N)(1.2 m)
W=23,520 J
P=W/t
P=23,520 J / 3600 s
P=6.53 W

14. Don’t forget to study the two Energy Transfer Model Packets so refresh on using LOL diagrams.

15. Don’t forget vocab and equation charts are due. Use flash cards!
Also add in conduction, convection, and radiation!!!

16. 1st law of Thermodynamics
"thermo," meaning heat, and "dynamic," meaning power
The First Law of Thermodynamics, commonly known as the Law of Conservation of Matter, states that matter/energy cannot be created nor can it be destroyed.
The quantity of matter/energy remains the same. It can change from solid to liquid to gas to plasma and back again, but the total amount of matter/energy in the universe remains constant.

17. 2nd law of Thermodynamics
Commonly known as the Law of Increased Entropy.
While quantity remains the same (First Law), the quality of matter/energy deteriorates gradually over time.
How so? Usable energy is inevitably used for productivity, growth and repair.
In the process, usable energy is converted into unusable energy. Thus, usable energy is irretrievably lost in the form of unusable energy.
"Entropy" is defined as a measure of unusable energy within a closed or isolated system (the universe for example).
As usable energy decreases and unusable energy increases, "entropy" increases.
Entropy is also a gauge of randomness or chaos within a closed system.
As usable energy is irretrievably lost, disorganization, randomness and chaos increase.