This preview shows page 1. Sign up to view the full content.
7.68. Set Up:
The watt represents power as joules per second; so convert the unit of year to seconds for part (a).
For part (b), the rate of consumption is simply the power divided by the estimated number of consumers.
Solve: (a)
(b)
7.69. Set Up:
From Problem 7.68, the U.S. consumes
of power per year. The area required in
part (a) may then be calculated as
However, for an array efficiency of 25%, the radiative
power rate must be multiplied by 0.25 to account for power losses. For part (b), since the array is square,
and
the length of a side is simply
Solve: (a)
(b)
Reflect:
An array of this size is approximately equivalent to the state of Rhode Island and thus feasible.
7.70. Set Up:
The thermal energy is produced as a result of the force of friction,
The average thermal
power is thus the average rate of work done by friction or
where
is based on the initial and final
velocities.
Solve:
Reflect:
The power could also be determined as the rate of change of kinetic energy,
where the time is calcu
This is the end of the preview. Sign up
to
access the rest of the document.
This note was uploaded on 03/06/2009 for the course PHYS 114 taught by Professor Shoberg during the Spring '07 term at Pittsburg State Uiversity.
 Spring '07
 Shoberg
 Energy, Power, Work

Click to edit the document details