Chapter 5 Review

1. Chapter 5 Review • Work may be measured using units of: • Joules

2. Your friend claims to have invented a perpetual motion machine with an efficiency of 110 percent. You tell him his invention is impossible because it violates what law: • Law of Conservation of Energy

3. In science, work is defined as: • Force time distance that an object moves in the same direction

4. Efficiency can be defined as the ratio of: • Work output to Work input

5. An electric food processor uses 10 joules of electrical energy every second. Due to friction and other causes, the energy available to spin the blades to cut food is reduced to 5 joules per second. The efficiency of the food processor is: • Wo/Wi • 5 J/ 10J = 50%

6. Calculate the work needed to lift a block weighing 2 newtons a distance of 10 meters. • W=Fd • 2N(10m) = 20 N*m or 20 J

7. How much power is necessary to do 50 joules of work in 5 seconds? • P = W/t • 50 J / 5 s = 10 W

8. A gallon of gasoline contains chemical energy. If you pour a gallon of gasoline into your car, you could drive for about 20 miles on the highway (about 20 minutes). You could choose instead to run a lawn mower for an hour with one gallon of gasoline. If the gasoline were to come in contact with a fire, the entire gallon would burn in less than a minute. Which reaction has the most power? • A. Burning the gasoline in the car • B. Burning the gasoline in a fire • C. Burning the gasoline in the lawn mower • D. They are equal because the gasoline has the same chemical potential energy in each case. • B

9. The efficiency of most machines is less than 100 percent. Due to friction, energy seems to be lost. While the energy is not truly lost, it does work that is not useful or is converted to: • Thermal energy or heat

10. A marble rolls along the track below with no friction. The sequence of positions on the track listed in order from the lowest kinetic energy to the highest kinetic energy is: • 1, 5, 4, 2, 3, 6

11. A moving car has kinetic energy. To bring the car to rest, you must decrease its kinetic energy to zero. The brakes do this work by applying a force over a distance. What effect would doubling the speed have on the braking distance? • A. The braking distance would be 4 times smaller. • B. The braking distance would be 2 times smaller. • C. The braking distance would be 2 times greater. • D. The braking distance would be 4 times greater. • D

12. Potential energy is energy due to the: • Height or position of an object

13. Exercise may transform the chemical energy in the food you eat into what two types of energy: • KE and PE

14. The amount of work performed over time • Power

15. The ability to do work • energy

16. Work done by a machine • Work output

17. Applied force that moves an object in the direction of the applied force. • Work

18. This is traded for force to achieve a mechanical advantage of more than one • distance

19. Work put into a machine • Work input

20. Ratio of the work output to the work input. • Efficiency

21. Formulas you will need to complete the test. • P = W/t • W = f x d • Ek= (½)mv2 • Ep = mgh • E = Wo/Wi x 100