Power
Power is the rate at which energy is used or the rate at which work is done.
Mathematically, the above statement can be expressed as:
In symbols, this expression is written as:
The unit of power is the WATT, (W)
1 W = 1 J/s
Example:
A crane lifts a 250 Kg crate of roof shingles from the ground on top of a 15 m high roof in 20 s. How much power did the crane use up?
Given:
m = 350 Kg
g = 9.8 m/s2
h = 15 m
t = 20 s
Find:
a) Force required
b) Work Done
c) Power
Solution:
a) The force Required to Lift Shingles up is the force of gravity, Fg
Fg = m x g (the force of gravity)
= 350 Kg x 9.8 N/Kg
= 3430 N
b) Work Done = Work Done in lifting
= Fg x h
= 3430 N x 15 m
= 51 450 Nm
= 51 450 J
c) Power = Work / time
= W / t
= 51 450 J / 20 s
= 2573 W