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Power is the rate at which energy is used up or work is done.
Mathematically, the above statement can be expressed as
In symbols, this expression is written as
and 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?
Solution:
Given: m =
350 Kg Find: a) Force required (See also
Forces)
g = 9.8 m/s2
b) Work Done (See also Energy and
Work)
h = 15 m
c) Power
t = 20 s
Solution: a) Force Required to
Lift Shingles up = 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
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