CHAPTER 17
PROBLEM 17.1
A 200-kg flywheel is at rest when a constant 300 N m
couple is applied. After executing 560 revolutions, the
flywheel reaches its rated speed of 2400 rpm. Knowing that the radius of gyration of the flywheel is 400 mm,
determine the average magnitude of the couple due to kinetic friction in the bearing.
PROBLEM 17.2
The rotor of an electric motor has an angular velocity of 3600 rpm when the load and power are cut off. The
110-lb rotor, which has a centroidal radius of gyration of 9 in., then coasts to rest. Knowing that the kinetic
friction of the rotor produces a couple of magnitude 2.5 lb ft,
determine the number of revolutions that the
rotor executes before coming to rest.
PROBLEM 17.3
Two uniform disks of the same material are attached to a shaft as shown.
Disk A has a weight of 10 lb and a radius r = 6 in. Disk B is twice as thick as
disk A. Knowing that a couple M of magnitude 22 lb ft is applied to disk A
when the system is at rest, determine the radius nr of disk B if the angular
velocity of the system is to be 480 rpm after 5 revolutions.
PROBLEM 17.4
Two disks of the same material are attached to a shaft as shown. Disk A has
radius r and has a thickness b, while disk B has radius nr and thickness 2b. A
couple M of constant magnitude is applied when the system is at rest and is
removed after the system has executed 2 revolutions. Determine the value of
n which results in the largest final speed for a point on the rim of disk B.
PROBLEM 17.4 (Continued)
Value of n for maximum final speed.
dn
PROBLEM 17.5
The flywheel of a small punch rotates at 300 rpm. It is known that 1800 ft lb of work must be done each time a
hole is punched. It is desired that the speed of the flywheel after one punching be not less that 90 percent of the
original speed of 300 rpm. (a) Determine the required moment of inertia of the flywheel. (b) If a constant 25-lb ft
couple is applied to the shaft of the flywheel, determine the number of revolutions which must occur between each
punching, knowing that the initial velocity is to be 300 rpm at the start of each punching.
PROBLEM 17.6
The flywheel of a punching machine has a mass of 300 kg and a radius of gyration of 600 mm. Each punching
operation requires 2500 J of work. (a) Knowing that the speed of the flywheel is 300 rpm just before a
punching, determine the speed immediately after the punching. (b) If a constant 25-N m couple is applied to
the shaft of the flywheel, determine the number of revolutions executed before the speed is again 300 rpm.
PROBLEM 17.7
Disk A, of weight 10 lb and radius
6r
in., is at rest when it is placed in
contact with belt BC, which moves to the right with a constant speed
40v
ft/s. Knowing that
0.20
k
between the disk and the belt, determine the
number of revolutions executed by the disk before it attains a constant
angular velocity.
PROBLEM 17.8
The uniform 4-kg cylinder A, of radius r 150 mm, has an angular velocity 0
=
50 rad/s when it is brought into contact with an identical cylinder B which is at rest.
The coefficient of kinetic friction at the contact point D is .
k
After a period of
slipping, the cylinders attain constant angular velocities of equal magnitude and
opposite direction at the same time. Knowing that cylinder A executes three
revolutions before it attains a constant angular velocity and cylinder B executes one
revolution before it attains a constant angular velocity, determine (a) the final
angular velocity of each cylinder, (b) the coefficient of kinetic friction .
k