1. Chapter 6.1 Notes Power

2. The time it takes to complete an activity is as important as the work required. Compare running up stairs to walking up stairs. When you run, you do the work faster. The rate of doing work or expending energy is power.

3. Work requires that an object moves. Power is a measurement of how fast something moves. Units for power is watts.

5. Power equation if work is known= Power = Work / time P = W / t

6. An engine does 5000 Newtons of work in 10 seconds. How much power is the engine doing? P = W/t P = 5000 J / 10 s P = 500 J/s or Watts

7. Power equation if force and distance are known = (Force x distance) / time P = (F x d) / t

8. To increase your power, you must increase Force or distance. To increase your power, you can also decrease the time.

9. A force of 20 Newtons moves a car a distance of 50 meters in 5 seconds. How much power was required? P = (F x d) / t P = (20 N x 50 m) / 5s P = (1000 Nm)/5s P = 200 Watts

10. Power when gravity is only force = (mass x gravity x distance) / time P = (m x g x d) / t

11. Mass of an elevator is 1200 kg. A motor raises the elevator 15 meters at a constant speed for 10 seconds. What is the power of the motor? P = (m x g x d) / t P = (1200 x 10 x 15) / 10 P = (180,000) / 10 P = 18,000 Watts

13. Power if a constant force other than gravity is at work = force x velocity P = f x v

14. A car has a drag force of 300 lbs and is capable of a constant velocity of 60 mph. How much power does the engine have? P = f x v P = 300 x 60 P = 18,000 Watt or HP

15. Not all energy or power is converted. Some is lost due to friction, air resistance, and gravity To find the efficiency of an engine’s power = Output Power / Input Power Eff = P o /P i

16. An elevator motor has an output power of 2 kW and an input power of 15 kW. What is the efficiency and percent efficiency? Eff = P o / P i Eff = 2/15 Eff =.13 or 13%

17. Power in a rotational system = Torque x angular speed P = t x w

18. The angular speed of a record is 750 rad/s. The Torque is.01 J. How much is the power of the record? P = t x w P =.01 x 750 P = 7.5 Watts