Mechanics & Wave Motion Problem Set 10

Y&F Chapter 10 on torque and angular momentum.  You can skip section 10.7  about gyroscope precession.  I went through this material pretty quickly in lecture, so this is a week where the book is really worth reading.

1. Assignment 10 on our MasteringPhysics course site.  It is longer than usual, so I'm making the written homework shorter in recompense.
2. Y&F end of chapter problems.
   1. 10.20.
   2. 10.42.
   3. 10.90.  Because some people (OK, it was only one person) liked the neutron star problem from last week.
   4. 10.92.  Hint:  Consider the block rotating in a circle as a single "body"; its moment of inertia will depend on R.  The only force on the block is the tension, but since the tension pulls directly toward the axis of rotation it causes no torque: therefore the angular momentum of the block is conserved throughout the whole process of pulling it closer to the central hole.  This allows you to calculate omega (or, equivalently, v) as a function of R.  Use the breaking strength of the string to give the centripetal acceleration at breakpoint.  Between these two equations (F = m a and L = constant) you can solve for R.