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

1 Horse Power = 746 Watts

Ex 1) 1440 kg car accelerates
from rest to 95 km/hr in 7.4 sec.
What average power is
used?

P = W/t

P = DKE/t

= 1/2m(V_{2}^{2
- }V_{1}^{2})/t

Convert km/hr

95 km/hr[1000m/km][hr/3600sec]

6.6 x 10^{4} W
or 88 hp

1 Horse Power = 746 Watts

P

=

W/t

=

Fd/t

=

Fv

(watt)

= (J/s)

(N)m/s

Ex 2) A 95 kg football player
runs up stairs in 66s. The stairs are 140 m long at an angle of 32°

Her power
output vertically is

P = W/t

P = Fd/t

F = [mgsinq]d/t

P = 1047 W

P = 1.0 x 10^{3} W

P

=

W/t

=

Fd/t

=

Fv

(watt)

= (J/s)

(N)m/s

P = Fd/t

Ex 3)1200 kg car has a max. power output of 120 hp. How
steep a hill can it climb at constant speed of 75 km/hr if the frictional
force is 650 N?