Download Sects. 5.3 through 5.4

Chapter 5 – part B
Non uniform circular motion
Velocity dependent resistive forces
Exercise 5.20
20.
A 4.00-kg object is attached
to a vertical rod by two strings as
shown in Figure P5.20. The object
rotates in a horizontal circle
at constant speed
6.00 m/s. Find the
tension in (a) the
upper string and
(b) the lower string.
Exercise 5.20
47.
In a home laundry dryer, a
cylindrical tub containing wet clothes is
rotated steadily about a horizontal axis
as shown in Figure P5.47. The clothes
are made to tumble so that they will dry
uniformly. The rate of rotation of the
smooth-walled tub is chosen so that a
small piece of cloth will lose contact
with the tub when the cloth is at an
angle of 68.0° above the horizontal. If
the radius of the tub is 0.330 m, what
rate of revolution is needed?
Exercise 5.47
50.
An air puck of mass m1 is tied to
a string and allowed to revolve in a
circle of radius R on a frictionless
horizontal table. The other end of the
string passes through a hole in the
center of the table, and a counterweight
of mass m2 is tied to it (Fig. P5.50). The
suspended object remains in equilibrium
while the puck on the tabletop revolves.
What are (a) the tension in the string,
(b) the radial force acting on the puck,
and (c) the speed of the puck?
Exercise 5.28
28.
A 9.00-kg object starting from
rest falls through a viscous medium


and experiences
a
resistive
force
R  bv

where v is the velocity of the object.
The object reaches one-half its
terminal speed in 5.54 s. (a) Determine
the terminal speed. (b) At what time is
the speed of the object three-fourths
the terminal speed? (c) How far has
the object traveled in the first 5.54 s of
motion?
Exercise 5.30
30.
Consider an object on which the
net force is a resistive force proportional
to the square of its speed. For example,
assume that the resistive force acting on
a speed skater is f = –kmv2, where k is a
constant and m is the skater’s mass. The
skater crosses the finish line of a straightline race with speed v0 and then slows
down by coasting on his skates. Show
that the skater’s speed at any time t after
crossing the finish line is
v(t) = v0/(1 + ktv0).