Physics 201 MWF10:20 Fall 1995 (Ford)
Exam III Chapts. 9,10,11,13 in SZY College Physics
Show all your work. Partial credit will be given if earned. Write your
answers in the blanks provided.
(16 pts) 1. A small object on a horizontal frictionless surface is attached to
a string that passes through a hole in the surface.
a) The object is originally revolving in a circle at a distance of 0.600 m
from the hole with an angular velocity of 2.0 rad/s.
What is the tangential velocity of the object?
Ans. ________________
b) The string is slowly pulled from below, shortening the radius of the circle
in which the object revolves. What is the new radius
r2 of the
circle in which the object revolves when the new angular velocity is
2 = 8.0 rad/s?
Ans. __________________
(22 pts) 2. A large cylinder with radius R = 0.12 m is pivoted
about a
stationary horizontal axis through the center of the cylinder. The
moment of inertia of the cylinder about this axis is 5.0 kg·m2.
The cylinder is free to turn without friction about this axis. A rope
of negligible mass is wrapped around the cylinder and a steady pull of
magnitude T is applied to the free end of the rope. The cylinder starts
from rest and turns through 6.0 revolutions in 3.0 s.
a) What is the angular acceleration 
of the
cylinder? (Express your answer in rad/s2.)
Ans. _______________
b) What is the angular velocity of the cylinder
after 3.0 s? (Express your answer in rad/s.)
Ans. _______________
c) What is the tension T in the rope?
Ans. _______________
d) How much work does the tension in the rope do during the 6.0
revolutions of the cylinder?
Ans. _______________
(24 pts) 3. A uniform bar 4.0 m long and weighing 60 N is attached at one
end to a wall by a frictionless hinge. A fish of weight w is suspended
from the bar, 3.0 m from the hinge. The bar is held in a horizontal
position by a wire that makes an angle of 37° with the bar and that
is attached to the end of the bar opposite the hinge. The tension in this
wire is 80 N.
a) What is the magnitude of the torque produced by the tension in the rope for
an axis at the hinge?
Ans. _________________
b) What is the weight w of the fish?
Ans. _________________
c) What are the vertical (Hv) and horizontal
(Hh) components of the
force that the hinge exerts on the bar?
Ans. Hv = _______________
Hh = __________________
(18 pts) 4. A block of mass m = 0.40 kg on a horizontal frictionless
surface is
attached to a horizontal spring. The block is moving in simple harmonic motion
with amplitude A = 0.30 m. When the block is at x = +0.10 m, its
speed is v = 5.0 m/s.
a) What is the force constant k of the spring?
Ans. ________________
b) When the block is at x = +0.10 m, what is its acceleration?
Ans. ____________________
c) What is the maximum speed of the block? At what value of x does it
occur?
Ans. vmax = ___________________
at x = ___________________
(20 pts) 5. A rock with volume 3.0×10-4 m3 is
suspended from a string.
a) When the rock is in air, the tension in the string is 7.0 N. What is
the density of the rock?
Ans. _______________________
b) The rock is completely immersed in water, but doesn't touch the bottom of
the water container. What is then the tension in the string? (The density of
water is 1000 kg/m3.)
Ans. _____________________
c) The rock is completely immersed in an unknown liquid and the tension in the
string is 5.4 N. What is the density of the unknown liquid?
Ans. ____________________