Physics 112 Discussion Notes: Week 1 (Spring 2004)

PHY218 SPRING 2015
RECITATIONS PROBLEMS: Week 10
Rotational mechanics
These are the problems that you and a team of other 2-3 students will be asked to solve during the recitation
session next week. Your team can do better if you think about the approach and explanation for these problems
BEFORE coming to class.
1. Two metal disks: Two metal disks, one with radius
c) Repeat the calculation of part b), this time
with the string wrapped around the edge of
the larger disk.
R1 and mass M1 and the other with radius R2 and
mass M2, are welded together and mounted on a
frictionless axis through their common center.
a) What is the total moment of inertia of the
two disks?
b) A light string is wrapped around the edge of
the smaller disk, and a block of mass M,
suspended from the free end of the string. If
the block is released from rest at a distance
of H above the floor, what is its speed just
before it strikes the floor?
M
2. Falling Meter Stick: A uniform meter stick of mass m is
attached to the wall by a frictionless hinge at one end. On
the opposite end it is supported by a vertical massless
string such that the stick makes an angle of θ with the
horizontal.
a) Find the tension in the string and the magnitude
and direction of the force exerted on the stick by
the hinge.
b) Suppose the string is cut. Find the angular
acceleration of the stick immediately thereafter.
Supplementary challenge
An inhomogeneous sphere: A sphere with radius R has density ρ that decreases with distance r from the center of the
sphere according to ρ=A−Br, where A and B are positive constants.
a) What are the units for the constants A and B?
b) Calculate the total mass of the sphere.
c) Calculate the moment of inertia of the sphere for an axis along a diameter.
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PHY218 SPRING 2015
RECITATIONS PROBLEMS: Week 10
Approach: Under this tab, list the steps taken by your team for finding each solution. You answer here the questions
WHAT? and HOW?
Approach 1.
Approach 2.
Explanation: Under this tab, explain why your team has chosen those approaches. You answer here the questions
WHY? and WHEN?
Explanation 1.
Explanation 2.
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