Turning which gear would give you
a mechanical advantage?
William Dwight Whitney The Century Dictionary and Cyclopedia: An
encyclopedic Lexicon of the English Language. (New York: The Century
Co., 1889)4499
Copyright: 2009, Florida Center for Instructional Technology. See
license.
Small Gear
C) Power - rate of doing work or expending energy
| P | = | W/t | = | Fd/t | = | Fv |
| (watt) | = (J/s) | (N)m/s |
Scalar
|
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 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?
| P | = | W/t | = | Fd/t | = | Fv |
| (watt) | = (J/s) | (N)●m/s | (N)●m/s |
= Fv = (40 N)(5 m/s) =
200 Nm/s
or 200 watts
|
Ex 2) A girl weighing 500. newtons takes 50. seconds to climb a flight of stairs 18 meters high. Her power output vertically is |
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. secs d = 18 m P = ? |
|
| P | = | W/t | = | Fd/t | = | Fv |
| (watt) | = (J/s) | (N)m/s |
P = Fd/t
P = 500. N(18. m)/50. sec
P = 180 Nm/sec = 180 watts
|
Ex 3)
A 95-kg student climbs 4.0 m up a rope in 3.0
seconds. |
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 sec P = ? |
|
| P | = | W/t | = | Fd/t | = | Fv |
| (watt) | = (J/s) | (N)m/s |
P = Fd/t
First find F (weight)
F = mg = 95 kg(10. m/s2)
= 950 N
P = 1.3 x 103 W
(Rounded to 2 significant digits)