2. Power

3. Power is defined as “Work per unit time”

4. Power is defined as “Work per unit time”
Units: J/s = 1 W (Watt)
(1 hp = 746 W)

5. Power Power is defined as “Work per unit time”
Units: J/s = 1 W (Watt)
What does the “Power Company” sell you?

6. Power Power is defined as “Work per unit time”
Units: J/s = 1 W (Watt)
What does the “Power Company” sell you?
What is a “kilowatt-hour”?

7. A light bulb consumes 3600 J of electrical energy every minute that it’s on. What is the power rating of this light bulb?
A) 36 W
B) 60 W
C) 100 W
D) 360 W
E) W

8. When a person runs up a flight of stairs, she does work mgh
When a person runs up a flight of stairs, she does work mgh. The power she generates depends on how long it takes to go from the bottom to the top. h

9. When a person runs up a flight of stairs, she does work mgh
When a person runs up a flight of stairs, she does work mgh. The power she generates depends on how long it takes to go from the bottom to the top.
Let’s do it! h

10. When passing a tractor on the highway, you accelerate your 1
When passing a tractor on the highway, you accelerate your 1.80 x 103 kg car from 26.8 m/s to 31.5 m/s in 2.75 s.
What power is required to do this?

11. While the engine is doing positive work on the car, friction and air resistance are doing negative work. K
engine
The rate at which friction and air resistance do work depends on the speed of the car.
When they are doing work at the same rate, the car’s speed won’t change.
A higher power engine allows the engine to do work at a higher rate, allowing for a higher top speed.
heat

12. As a car drives up a hill, it has to overcome gravity, friction, and air resistance. The power required to do that depends on velocity…
(It’s a bit more complicated than it looks, since air resistance goes up with speed or speed2)

13. It takes a force of 1450 N to keep a 1300 kg car moving with constant speed up a slope of 5.25˚. If the engine delivers 4.10 x 104 W (55 hp) to the drive wheels, what is the maximum speed of the car?