Engineering Fundamentals: An Introduction to Engineering, 4th ed.c

410 Chapter 13 Energy and Power

Summary

Now that you have reached this point in the text

• You should understand how different forms of mechanical energy are defined. You should
  know how and when to use kinetic energy, potential energy, and elastic energy in engineer-
  ing analyses.


• You should know what is meant by internal energy and heat.


• You should know how and when to use conservation of energy to solve engineering problems.


• You should clearly understand the definition of power, its common units, and how it is related
  to work and energy.


• You should know the basic definition of efficiency and be familiar with its various forms,
  including the definitions of thermal efficiency, SEER, and AFUE, which are commonly used
  to express the efficiencies of components such as pumps, compressors, and motors, as well as
  complete systems including heating, ventilating, and air-conditioning (HVAC) equipment
  and household appliances.

Problems

13.1. Identify ways that you can save energy. For example,

walking up a floor instead of taking the elevator, or

walking or riding your bike an hour a day instead of

taking the car. Estimate the amount of energy that you

could save every year with your proposal. Also, estimate

the amount of fuel that can be saved in the same man-

ner. State your assumptions, and present your detailed

analysis in a report.

13.2. Look up the manufacturer’s data for the most recent

year of the following cars:

a. Toyota Camry

b. Honda Accord

c. BMW 750 Li

You can visit the cars.com Website to gather information.

For each car, perform calculations similar to Example 13.9

to determine the power required to accelerate the car from

0 to 60 mph. State all of your assumptions.

13.3. An elevator has a rated capacity of 2000 lb. It can trans-

port people at the rated capacity between the first and

the fifth floors, with a vertical distance of 15 ft

between each floor, in 7 s. Estimate the power require-

ment for such an elevator.

13.4. Determine the gross force needed to bring a car that

is traveling at 110 km/h to a full stop in a distance of

100 m. The mass of the car is 2100 kg. What happens

to the initial kinetic energy? Where does it go or to

what form of energy does the kinetic energy convert?

13.5. A centrifugal pump is driven by a motor. The perfor-

mance of the pump reveals the following information:

Power input to the pump by the motor (kW):

0.5, 0.7, 0.9, 1.0, 1.2

Power input to the fluid by the pump (kW):

0.3, 0.55, 0.7, 0.9, 1.0

Plot the efficiency curve. The efficiency of a pump

is a function of the flow rate. Assume that the flow-

rate readings corresponding to power data points are

equally spaced.

13.6. A power plant has an overall efficiency of 30%. The

plant generates 20 MW of electricity, and uses coal

from Montana (see Table 11.12) as fuel. Determine

how much coal must be burned to sustain the genera-

tion of 20 MW of electricity.

13.7. Estimate the amount of gasoline that could be saved

if all of the passenger cars in the United States were

driven 1000 miles less each year. State your assump-

tions and write a brief report discussing your

findings.

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