Unlock document.
This document is partially blurred.
Unlock all pages and 1 million more documents.
Get Access
PROBLEM 8.95*
Assuming that bearings wear out as indicated in Problem 8.94, show that the magnitude M of the couple
required to overcome the frictional resistance of a worn-out collar bearing is
1
12
2
()
k
MPRR
where P magnitude of the total axial force
R
1
, R
2
inner and outer radii of collar
PROBLEM 8.96*
Assuming that the pressure between the surfaces of contact is uniform,
show that the magnitude M of the couple required to overcome frictional
resistance for the conical bearing shown is
33
21
22
21
2
3sin
k
PRR
MRR
PROBLEM 8.97
Solve Problem 8.93 assuming that the normal force per
unit area between the disk and the floor varies linearly
from a maximum at the center to zero at the
circumference of the disk.
PROBLEM 8.93
A 50-lb electric floor polisher is
operated on a surface for which the coefficient of
kinetic friction is 0.25. Assuming that the normal force
per unit area between the disk and the floor is
uniformly distributed, determine the magnitude Q of the
horizontal forces required to prevent motion of the
machine.
PROBLEM 8.97 (Continued)
PROBLEM 8.98
Determine the horizontal force required to move a 2500-lb automobile with 23-in.-diameter tires along a
horizontal road at a constant speed. Neglect all forms of friction except rolling resistance, and assume the
coefficient of rolling resistance to be 0.05 in.
PROBLEM 8.99
Knowing that a 6-in.-diameter disk rolls at a constant velocity down a 2 percent incline, determine the
coefficient of rolling resistance between the disk and the incline.
PROBLEM 8.100
A 900-kg machine base is rolled along a concrete floor using a series of
steel pipes with outside diameters of 100 mm. Knowing that the
coefficient of rolling resistance is 0.5 mm between the pipes and the
base and 1.25 mm between the pipes and the concrete floor, determine
the magnitude of the force
P
required to slowly move the base along the
floor.
PROBLEM 8.101
Solve Problem 8.85 including the effect of a coefficient of rolling resistance of 1.75 mm.
PROBLEM 8.85
A scooter is to be designed to roll down a 2 percent slope at a constant speed.
Assuming that the coefficient of kinetic friction between the 25-mm-diameter axles and the bearings is
0.10, determine the required diameter of the wheels. Neglect the rolling resistance between the wheels
and the ground.
PROBLEM 8.102
Solve Problem 8.91 including the effect of a coefficient of rolling resistance of 0.5 mm.
PROBLEM 8.91
A loaded railroad car has a mass of 30 Mg and is supported by eight 800-mm-diameter
wheels with 125-mm-diameter axles. Knowing that the coefficients of friction are
0.020
s
and
0.015,
k
determine the horizontal force required (a) to start the car moving, (b) to keep the car moving at a constant
speed. Neglect rolling resistance between the wheels and the track.
PROBLEM 8.103
A rope having a weight per unit length of 0.4 lb/ft is wound 2 2
1 times
around a horizontal rod. Knowing that the coefficient of static friction
between the rope and the rod is 0.30, determine the minimum length x of
rope that should be left hanging if a 100-lb load is to be supported.
