Physics 4A--Exam 4 Sample Problems
A
2 kg uniform rod of length 1m is constrained to rotate about a horizontal axis
passing through its center. The rod has a 1.5 kg point mass attached to one
end and a 0.5 kg point mass attached to the other end. The 1.5 kg mass is given
a downward push so that it starts moving with an initial velocity of 1.2 m/s.
a. Find the moment of inertia of the system.
b. Find the initial kinetic energy of the system.
c. Through what total angle does the system rotate through before coming to rest?
A 3 kg mass attached to a spring undergoes SHM on a frictionless horizontal
surface. The period of the motion is 4.5 s. If the mass was originally pulled
back 12 cm from the equilibrium position, find the
a. total energy of the system.
b. the maximum velocity of the mass.
c. the position of the mass when one half the total energy is in potential form.
d. Write an equation for the position of the mass as a function of time.
A satellite of mass m is to be placed in a circular orbit so that the satellite is a distance of 2Re above the surface of the earth. (Leave all answers in terms of Re, Me, and G.)
a. What minimum amount of work must be done to lift the satellite into this orbit? Hint: Find the change in energy.
b. What minimum initial speed would the satellite need to leave from its orbit and completely escape from the earth?
A solid disk of mass M and radius R is free to rotate about a fixed axis through
the point O which passes through the center of mass of the disk. A mass m hangs
by a string which is wrapped around the rim of the disk. If the system starts
from rest, find the velocity of the hanging mass after it has fallen through
a vertical height h. Solve the problem by using
a. Newton's 2nd Law
b. Conservation of energy
A sphere of radius 0.4 m is released from rest and rolls down an inclined plane
as shown.
a. Find the velocity of the center of mass of the sphere when it has traveled
a distance of 8 m along the incline. Use conservation of energy in your solution.
b. From your answer in part a determine the angular acceleration experienced
by the sphere.
What would happen to the acceleration of gravity at the surface of the earth
if the mass of the earth increased by 20% and its radius decreased by 20%?
A disk-shaped cloud of hydrogen with mass 1030 kg and radius 108
km rotates about an axis through the center of the disk as shown with a period
of 1000 days. After a long time, the disk contracts into a spherical star of
radius 106 km. What is the new period of rotation?
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