226 Chapter 8 Time and Time-Related Parameters
30 ft/s
30 ft/s
18 14
8 10
8 10
Problem 8.27
60
20 1220
Time (s)
1230
Speed (mph)
Problem 8.28
8.27.Consider the duct system shown in the accompanying
figure. Air flows through two 8-in.-by-10-in. ducts that
merge into a 18-in.-by-14-in. duct. The average speed
of the air in each of the 8 10 ducts is 30 ft /s. What
is the volume flow rate of air in the 18 14 duct?
Express the volume flow rate in ft
3
/s, ft
3
/min, and m
3
/s.
What is the average speed of air in the 18 14 duct?station, measure the volumetric flow rate of the gas
first, and then measure the diameter of the nozzle. Use
Equation (8.12) to calculate the average speed of
the gasoline coming out of the nozzle.Hint:First mea-
sure the time that it takes to put so many gallons of
gasoline into the gas tank!
8.17. Measure the volumetric flow rate of water coming out
of a faucet. Also determine the average velocity of water
leaving the faucet.
8.18. Determine the speed of a point on the earth’s surface in
ft /s, m/s, mph, km/h. State your assumptions.
8.19. Into how many time zones are the United States and its
territories divided?
8.20. Estimate the rotational speed of your car wheels when
you are traveling at 60 mph.
8.21. Determine the natural frequency of a pendulum whose
length is 5 m.
8.22. Determine the spring constant for Example 8.1 if the
system is to oscillate with a natural frequency of 5 Hz.
8.23. Determine the traffic flow if 100 cars pass a known
location during 10 s.
8.24. A conveyer belt runs on 3-in. drums that are driven by
a motor. If it takes 6 s for the belt to go from zero to
the speed of 3 ft /s, calculate the final angular speed of
the drum and its angular acceleration. Assume constant
acceleration.
8.25. Chinook, a military helicopter, has two three-blade
rotor systems, each turning in opposite directions.
Each blade has a diameter of approximaterly 41 ft. The
blades can spin at angular speeds of up to 225 rpm.
Determine the translational speed of a particle located
at the tip of a blade. Express your answer in ft /s, mph,
m/s, and km/h.
8.26. Consider the piping system shown in the accompany-
ing figure. The speed of water flowing through the
4-in.-diameter section of the piping system is 3 ft /s.
What is the volume flow rate of water in the piping sys-
tem? Express the volume flow rate in ft
3
/s, gpm,
and L /s. For the case of steady flow of water through
the piping system, what is the speed of water in the
3-in.-diameter section of the system?4 in. 3 ft/s 3 in.
Problem 8.26
8.28. A car starts from rest and accelerates to a speed of
60 mph in 20 s. The acceleration during this period is
constant. For the next 20 minutes the car moves with
the constant speed of 60 mph. At this time the driver
of the car applies the brake and the car decelerates to a
full stop in 10 s. The variation of the speed of the car
with time is shown in the accompanying diagram.
Determine the total distance traveled by the car and
the average speed of the car over this distance. Also plot
the acceleration of the car as a function of time.Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).圀圀圀⸀夀䄀娀䐀䄀一倀刀䔀匀匀⸀䌀伀䴀圀圀圀⸀夀䄀娀䐀䄀一倀刀䔀匀匀⸀䌀伀䴀