1 / 16

Power

Power. Chapter 5.6 WOD is underlined. Question. A 2400 kg car can slow from 10 m/s to rest in 3.2 meters. If the car has traditional friction brakes, what force do they apply while decelerating? (Show how to get vf^2 = vi^2 + 2av from w = Delta KE). Question.

clovis
Télécharger la présentation

Power

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Power • Chapter 5.6 • WOD is underlined

  2. Question • A 2400 kg car can slow from 10 m/s to rest in 3.2 meters. If the car has traditional friction brakes, what force do they apply while decelerating? • (Show how to get vf^2 = vi^2 + 2av from w = Delta KE)

  3. Question • If this same car is traveling at 15 m/s, what will the stopping distance be? • At 20 m/s? • 25 m/s? • 30 m/s?

  4. Show that • Vel vs distance is a • Quadratic function. • Can also solver eqn. • Relate to a student • Speeding at 95 vs 65. • Speed increase is 50%. • Distance increase is 100%

  5. Power • Power is work / time • P = W / t • Power is Capital P • Do not confuse this with lowercase p • (p = rho = momentum)

  6. Power Add units to WOD. • Power is work / time • P = W / t • Units are Joules/seconds or “Watts” • 1 Watt = 1 kg m2/s3 • 1 W = 1 J / s • The concept of POWER focuses on TIME. • English units is horsepower. • Based upon actual power 1 horse can generate.

  7. Power Add units to WOD. • Power is work / time • P = W / t • Do Power companies sell us power?

  8. Power Add units to WOD. • Power is work / time • P = W / t • Do Power companies sell us power? • No, Power is kWatts. • They sell us kW-Hours. • P * time = (Work / time) * time • = Work = Energy

  9. Power • Question: If someone uses 1000 watts of power for one hour, how much energy do they use? • (shown next slide)

  10. Power • Question: If someone uses 1000 watts of power for one hour, how much energy do they use? • (Work out here) • P = 1000 watts • = 1000 J /s • Problem is 1000 J /s * 1 h • = 1000 J/s * 3600 s/hr * 1 h

  11. Power • Question: If someone uses 1000 watts of power for one hour, how much energy do they use? • 3.6 * 10 6 Joules

  12. Different Units: • American Unit is “Horse Power” or “Power supplied by one horse” • 1hp = 550 foot*lbs/second • 1 hp = 746 Watts • Also, energy can be measured in KiloWatt Hours • 1 kwh = 3.6 * 10 6 Joules • Kwh = power * time = energy • Your electric bill probably uses kwh instead of Joules

  13. If you run your hair dryer for 20 minutes at 1500 watts at 12 cents a kWh. How much did you spend? Cost = kW * hr * $ /kWh * 30 days = 1.5 * 20/60 * .12 * 30 = $1.80 How about switching 15 light bulbs from 100 watt to 13 watt? Watt savings is 15*(100-13) =1305W= 1.3 kW Cost = kW * hr * $ /kWh * 30 days = 1.3 * 8 hr/day * .12 * 30 = $37.44

  14. How about switching off your computer and monitor? How much do you save? Those use about 250w/hr each. Assume you turn it off 20 hours a day instead of leaving it on all the time. • Know for test: Cost = kW * hr * $ /kWh • Like test question, calculate for 1 day. • Cost = kW * hr * $ /kWh = .500 * 20 hr/day * .12 = $1.2/day Savings on utility bill by turning it off for the 20 hours a day that the computer sits idle = $1.2/day * 30 = $36 a month

  15. Problem • An elevator must lift 1000 kg mass a distance of 100 m at a velocity of 4 m/s. What is the average power the elevator exerts during this trip?

  16. Problem • An elevator must lift 1000 kg mass a distance of 100 m at a velocity of 4 m/s. What is the average power the elevator exerts during this trip? • Power = work / time = mgh/t = mg (h/t) = mg*v = 1000 kg (9.8m/s2) (4m/s) = 39200 watts

More Related