Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Speed of object falling from pulley

  1. Nov 30, 2005 #1
    A uniform circular shell of mass M and radius R rotates about a vertical axis on frictionless bearings. A massless cord passes around the equator of the shell, over a pulley of rotational inertia I and radius r, and is attached to a small object of mass m. There is no friction on the pulleys axle; the cord does not slip. What is the speed of the object after it falls a distance h from rest? Use energy considerations.

    I dont really know where to start, can anyone point me in the right direction?
  2. jcsd
  3. Nov 30, 2005 #2

    Chi Meson

    User Avatar
    Science Advisor
    Homework Helper

    Sure. Use energy considerations.

    What form of energy does the mass have before it falls, and how much?

    What will be the forms of energy present after the mass has fallen "h"?
    Last edited: Nov 30, 2005
  4. Nov 30, 2005 #3
    would it have gravitational potential energy?

    Im not sure after..
  5. Nov 30, 2005 #4

    Chi Meson

    User Avatar
    Science Advisor
    Homework Helper

    Yes, gravitational potential, mgh right?

    Now after this hanging mass has torqued the sphere, what TWO things are moving, and what kind of energies do they have? OK, what kind of kinetic energies do they have?
  6. Nov 30, 2005 #5
    what two things are moving? the mass and the sphere?

    What kind of kinetic energies? I have no clue?
  7. Nov 30, 2005 #6
    Can someone please help me..this is the last question I need help solving!!
  8. Nov 30, 2005 #7
    the mass falls. what does that do to the string? what does the string do to the sphere?
    so then whats the total kinetic energy?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook