APES Energy Problems
Energy Problems – Part 1
Name______Date______PER______ST#______
Energy: The basic unit of energy is a Joule (J). Other units are calorie, kilojoule, British Thermal Unit (BTU), and therm. Energy is the ability to do work. (memorize that definition!)
· 1 Joule is the energy required to exert 1 Newton of force for one meter (or to move .22 pounds for one meter)
· 1000J = 1 kJ
· 1 calorie (small C, the science calories) is the energy to raise 1 gram of water one degree Celsius.
· 1000cal = 1kcal (or 1 Cal, the “dietary” calories that are on food labels)
· 1 cal = 4.184 J, so 1 Cal = ______FILL IN THE BLANK!!!!!
· A BTU is the energy required to raise one pound of water by one degree Fahrenheit.
· 1 BTU = 1.05 kJ
· 1 therm = 100 ft3 = 1CCF = 100,000 BTU [it’s sold to us in CCF (hundred cubic feet) or MCF (a MCF is 10 CCF’s or 1,000 ft3) , a CCF costs about $1, so an MCF costs about $______]
1. If I eat a typical adult male diet of 2000 Calories a day, how many calories is that?
2. 1 BTU = 1.05 kJ, so how many Joules are in 1 BTU? (convert “kilo” and you have the answer)
3. Use your answer for #2 to determine how many BTUs are in a Joule.
4. Use your previous answers to determine how many calories (science) are in a BTU.
5. Now determine how many Calories (dietary) are in a BTU.
6. The shower question:
a. If your 20-minute, nice-and-hot shower empties the 40 gallon water tank at home, and it takes about 20 cents worth of gas to heat all of that water, how many CCF of natural gas did you use? How many cubic feet of gas is that?
b. How many BTUs of gas did you use for your shower in part “a?”
c. How many calories and Calories would it take to heat the water for the shower?
d. When it comes to showers, how can you save money and reduce your impact on the environment at the same time?
e. Shorter showers save on at least 3 other things (not just the heat for the water), what can you think of for those savings?
You have to do this side of the page on a separate sheet of paper!!!
Power: Power is the rate at which energy is used, or the rate at which work is done. The equation can be written as P = E/t, which means power = energy / time. Since it involves the ability to do work, the equation is usually written as P = w/t, which is power = work / time
Example: How many watts of power are used to do one Joule of work in one second?
P = w/t
P = 1 Joule / 1 second
P = 1J/s (same thing as the previous line in the problem, I’m just showing you abbreviations)
P = 1 Watt (since 1Watt = 1 Joule per second, by definition)
1W = 1J/s (1Watt = 1 Joule per second, again -the definition of a Watt)
1. An incandescent 100 Watt bulb uses 100 J/sec of electrical energy.
a. Complete a P = w/t problem to show how 100 J/s = 100 Watts
b. What is the equivalent number of food calories per second (Cal) that this bulb is using? Hint: you just need to convert the 100J to Cal!
c. How long could you keep a 100 Watt bulb burning if you could use the 1230 Calories in a Big Mac and Large Sized fries? Hint – break this problem down, and use the info from the last question to help with the calculation.
d. How much energy does the 100 W bulb use in 12 hours of operation?
e. If the incandescent bulb is 20% efficient, then the bulb converts 20% of the electrical energy into light and 80% is wasted by being transformed into heat (ever felt a hot light bulb?). How many of the Watts in the 100 Watt light bulb are actually used for generating light?
f. How much energy does the bulb convert to light during 12 hours?
g. Convert total energy use to kWh and determine the cost, if it is 13.5 cents per kWh
h. How much would it cost to use a 23 Watt CFL for the same amount of time?
2. CFL vs. incandescent – comparison.
a. If a 23 Watt compact fluorescent light bulb (CFL) is able to make the same amount of light as a 100W incandescent bulb, how much more efficient (%) is the CFL?
b. Go to http://www.thebulb.com/store/t-cflmath.aspx and write down how many pounds of CO2 are released while using the incandescent vs. the fluorescent bulb.
c. Why is there a focus on CO2 reduction?
d. In our personal lives, reducing CO2 may or may not mean anything to us in relation to question 3C, but considering that the CO2 comes from burning fuel, what is at least one other reason that it might be important? (Hint: think about “Sellin’ It”
e. Why did they leave the cost of the bulbs out of their calculation?
f. Should they have taken the environmental and monetary cost of making, transporting and stocking 10 incandescent bulbs and 1 CFL bulb into consideration?