Physics 107 HOMEWORK ASSIGNMENT #8
Cutnell & Johnson, 7th edition
Chapter 9: Problems 16, 22, 24, 60, 68
16 A lunch tray is being held in one hand, as the drawing
illustrates. The mass of the tray itself is 0.200 kg, and its
center of gravity is located at its geometrical center. On the
tray is a 1.00-kg plate of food and a 0.250-kg cup of coffee.
Obtain the force
exerted by the thumb and the force
exerted by the four fingers. Both forces act perpendicular to
the tray, which is being held parallel to the ground.
*22 The drawing shows an outstretched arm (0.61 m in
length) that is parallel to the floor. The arm is pulling
downward against the ring attached to the pulley system, in
order to hold the 98-N weight stationary. To pull the arm
downward, the latissimus dorsi muscle applies the force M in
the drawing, at a point that is 0.069 m from the shoulder joint
and oriented at an angle of 29°. The arm has a weight of 47 N
and a center of gravity (cg) that is located 0.28 m from the
shoulder joint. Find the magnitude of M.
*24 A woman who weighs 500N is leaning against a smooth vertical wall, as the
drawing shows. Find (a) the force FN (directed perpendicular to the wall) exerted
on her shoulders by the wall and the (b) horizontal and (c) vertical components of
the force exerted on her shoes by the ground.
**60 A small 0.500-kg object moves on a frictionless horizontal table in a circular path of
radius 1.00 m. The angular speed is 6.28 rad/s. The object is attached to a string of negligible
mass that passes through a small hole in the table at the center of the circle. Someone under the
table begins to pull the string downward to make the circle smaller. If the string will tolerate a
tension of no more than 105 N, what is the radius of the smallest possible circle on which the
object can move?
*68 A wrecking ball (weight = 4800 N) is supported by a boom, which may
be assumed to be uniform and has a weight of 3600 N. As the drawing
shows, a support cable runs from the top of the boom to the tractor. The
angle between the support cable and the horizontal is 32°, and the angle
between the boom and the horizontal is 48°. Find (a) the tension in the
support cable and (b) the magnitude of the force exerted on the lower end of
the boom by the hinge at point P.