1. GIG
Read the passage and mark your answers on your whiteboard. NOT ON THE PAPER.
Questions

2. Power

3. Power
Power is a measure of how much work is done within a given time. It is measure in watts (W).
The formula for power is:
P = W power = work / time t

4. Watts
A watt (W) is 1 joule per second.
1W = 1 J s

5. Sample Problem
An 80.0kg person climbs stairs, rising 3.7m vertically in 22s. How much power did the person apply?

6. Sample Problem
An 80.0kg person climbs stairs, rising 3.7m vertically in 22s. How much power did the person apply?
First find the force applied against gravity.
F = mg = 80.0kg ✕ 9.81m/s2 = 784.8N
Now find work.
W = Fd = 784.8N(3.7m) = 2904J

7. Sample Problem
An 80.0kg person climbs stairs, rising 3.7m vertically in 22s. How much power did the person apply?
Power = work / time
P = 2904J = 130W
22s

10. Try This on Your Whiteboard
The “fancy” car in the example used 40.9 horsepower. How fast can a 2021kg Dodge Challenger Hellcat, using all 797 horsepower, accelerate from 13.4m/s to 17.9m/s?
797hp = 594,323W

11. Try This on Your Whiteboard
The “fancy” car in the example used 40.9 horsepower. How fast can a 2021kg Dodge Challenger Hellcat, using all 797 horsepower, accelerate from 13.4m/s to 17.9m/s?
P = W/t
594,323W = .5(2021kg)(17.9m/s)2 - .5(2021kg)(13.4m/s)2 t
t = J = 0.239s
594323W

12. Another Way to Think of Power
If we rewrite P = W/t to include the definition of work (Fd),
we have
P = Fd = F(d/t) t
d/t is velocity, so it is also true that
P = Fv power = force times velocity

13. Solve These with your Teammates
Page 216, LessonCheck problems

14. Homework
Review your notes from unit 1. Test on block day next week.

15. Closure
In chapter 6, we learned that energy is conserved in a closed system and that we can calculate from energy to velocity. This will become important to collisions in chapter 7.