Physics 107 HOMEWORK ASSIGNMENT #8
Cutnell & Johnson, 7th edition
Chapter 9: Problems 16, 22, 24, 66, 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.
*66 The drawing shows a bicycle wheel resting against a small step whose
height is h = 0.120 m. The weight and radius of the wheel are W = 25.0 N and
r = 0.340 m. A horizontal force
is applied to the axle of the wheel. As the
magnitude of
increases, there comes a time when the wheel just begins to
rise up and loses contact with the ground. What is the magnitude of the force
when this happens?
*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.