1. Chapter 10 Practice!

2. A car uses only about 20% of the energy in gasoline to make the car move. What is this an example of?
EXPLAIN!

3. Is this statement true? “The amount of energy in a system stays the same”
EXPLAIN!

4. EXPLAIN! (using what you know about energy conversion!)
Is this statement true? “If 200 calories of ice cream is eaten, all of the energy is stored as fat”
EXPLAIN! (using what you know about energy conversion!)

5. Is this statement true? “Energy increases over time”
EXPLAIN!

6. Is energy “lost” in all conversions? What is this called?
EXPLAIN!

7. Is perpetual motion possible? What law would this defy?
EXPLAIN!

8. Define ENTROPY
Give an example.

9. You eat turtle soup for lunch
You eat turtle soup for lunch. The chemical energy from the turtle becomes ________ energy in your body
A. potential
B. kinetic
C. both Ep and Ek
D. neither Ep nor Ek

10. Both Ep and Ek!

11. Why do brakes on a car become hot?
Work _______ is being converted to _______ energy (heat).

12. Work OUTPUT is being converted to THERMAL energy (heat)

13. An automobile is about 12 percent efficient
An automobile is about 12 percent efficient. For every 10 gallons of fuel used by the car, the number of gallons actually used to move the vehicle is:

14. 1.2 gallons!
Output = Eff * Input
= .10 * 12
= 1.2 gallons

15. The efficiency of a bicycle is 92 percent
The efficiency of a bicycle is 92 percent. If you exert 250 joules in pedaling a bicycle on level ground, what is the work output?

16. 230 joules!
Output = Eff * Input
= .95 * 250
= 230 joules

17. An incandescent light bulb uses 100 joules of electrical energy every second. Due to heat loss, the energy available to light the room is reduced to 6 joules per second. The efficiency of the light bulb is ____ percent.

18. 6%!
Eff = output/input
= (6 joules/ 100 joules) *100
= 6% efficient

19. Steven Tyler uses 1,200 joules of energy to lift a 200-newton crate 5 meters using a pulley system. The efficiency of the system is ____ percent.

20. 83%! Eff = output/input Output work = F * d = 200 N * 5 m = 1000 J
Input work = what Steven uses
= 1200 J
Eff = (1000J/ 1200J) * 100
= 83%

21. You want to build a record-breaking coaster that goes 70 m/sec at the bottom of the first hill. You estimate that the efficiency of the tracks and cars you are using is 90%. How high must the first hill be?

22. How high must the first hill be?
You are asked to find h
Key word is “efficiency”
Always start with the base equation:
Input = Output/Eff…(h is in the Input)
mgh = (½mv²)/ Eff
Solve for h by dividing both sides by mg:
h = (½mv²/Eff) / mg
= 278 m

23. Snoop Dogg is pedaling down a steep hill on his bicycle and wants to be able to coast up the next hill, which is 25.0 meters high, without pedaling up the hill at all. What would his speed need to be, assuming his bike is 100% efficient? **LOL Model it!**

24. What would his speed need to be, assuming his bike is 100% efficient?
You are asked to find v
Key word is “efficient”
Always start with the base equation:
Output = Eff * Input…(v is in the output)
(½mv²) = 1 * mgh
Solve for v by dividing
v = √(1 * mgh) / (½m)
= 22.1 m/s

25. How much energy is needed to run a 150-watt nose hair trimmer for five seconds?

26. 750 joules!

27. How much energy is needed to run a 150-watt nose hair trimmer for five seconds?
You are asked to find energy
You are given watts and time
Hmmm….what equation does that fit?

28. How much energy is needed to run a 150-watt nose hair trimmer for five seconds?
Base equation:
Power = J/t
To solve for joules:
joules = P * t
= (150)(5)
= 750 J

29. If 60 watts of power are consumed in 20 seconds, the maximum work done is ____ joules.

30. 1200 J You are asked for joules You are given power and time
Base equation:
Power = joules/t
Solve for joules:
joules = P*t
= (60)(20)
= 1200 J

31. The power used in doing 700 joules of work in 30 seconds is ____ watts.

32. 23.3 watts!
P = J/t

33. An ice cream person lifts her ice cream a distance of 0
An ice cream person lifts her ice cream a distance of 0.5 meters using 25 joules of energy. Her ice cream has a mass of about ____ kilograms. **LOL Model it!**

34. 5kg!

35. What’s going on? Someone is lifting something…hmmm…WORK! Work = F * d
An ice cream person lifts her ice cream a distance of 0.5 meters using 25 joules of energy. Her ice cream has a mass of about ____ kilograms.
What’s going on? Someone is lifting something…hmmm…WORK!
Work = F * d
Force = work/d
Where’s the kg?.....hmmm….in the Force!
Force = kg * 9.8 so…..
kg * 9.8 = work/d
kg = (work/d)/9.8

36. If a 60,000-watt toy car were rated in horsepower, its rating would be about ____ horsepower.

37. 80.4 hp!
60,000 watts/ 746 watts