Power
The rate of doing work or expending energy
RIDDLE: Two girls race up two flights of stairs, and it ends in a tie. Why does one racer claim that she was the more powerful racer?
Turning which gear would give you a mechanical advantage?
ETC Clipart — William Dwight Whitney, The Century Dictionary and Cyclopedia (New York: The Century Co., 1889) 4499. Copyright: 2009, Florida Center for Instructional Technology. See license.
Large Gear
C) Power
rate of doing work or expending energy
“… radically improved the power, efficiency, and cost-effectiveness of steam engines.” He developed the concept of horsepower, and the SI unit of power, the watt, was named after him. — Wikipedia
Ex 1
A force of 40 N is exerted on a mass, causing it to move with a constant speed of 5 m/s.
What power is used?
Ex 2
A girl weighing 500. newtons takes 50. seconds to climb a flight of stairs 18 meters high.
Her power output vertically is…
F = 500. N
t = 50. s
d = 18 m
P = ?
Ex 3
A 95-kg student climbs 4.0 m up a rope in 3.0 seconds.
What is the power output of the student?
m = 95 kg
d = 4.0 m
t = 3.0 s
P = ?
Check Your Understanding
5 quick questions — pick an answer to see if you’re right.
1. Power is defined as
2. Which unit is equivalent to a watt?
3. A 40 N force moves a crate at a constant speed of 5 m/s. What power is used?
4. A girl weighing 500. N climbs stairs 18 m high in 50. s. What is her vertical power output?
5. Two girls race up the same flight of stairs and tie. Which girl developed more power?
