1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Hollow sphere rolling down a slope

  1. Nov 19, 2011 #1
    1. The problem statement, all variables and given/known data
    A hollow, spherical shell with mass 2.50kg rolls without slipping down a slope angled at 35.0 degrees.
    i) Find the acceleration
    ii) Find the friction force
    iii) Find the minimum coefficient of friction to prevent slipping


    2. Relevant equations

    [itex]F=ma[/itex]

    [itex]I=\frac{2MR^2}{3}[/itex]

    Energy must stay constant:
    [itex]E_{p}+E_{kr}+E_{k} = E_{p}+E_{kr}+E_{k}[/itex]

    [itex]mgh+\frac{1}{2}Iw^{2}+\frac{1}{2}mv^{2}=mgh+\frac{1}{2}Iw^{2}+\frac{1}{2}mv^{2}[/itex]

    3. The attempt at a solution
    I really have no idea where to start, because a radius is not given, so I cannot find the moment of inertia. I was thinking if I used the energies, and said that

    [itex]mgh=\frac{1}{2}mv^{2}+\frac{1}{2}Iw^{2}[/itex]

    [itex]mgh=\frac{1}{2}mv^{2}+\frac{1}{2}((\frac{2}{3}mR^2)w^{2}[/itex]

    because we could use a pretend example, say that the sphere starts at rest at the top of the ramp, and in the end, all the energy is kinetic. But from here, I'm not really sure where to go. Thanks!
     
  2. jcsd
  3. Nov 19, 2011 #2

    Delphi51

    User Avatar
    Homework Helper

    Who knows, maybe it will turn out that the radius doesn't matter! If not, then an R in the answers will be expected. Go ahead and do it with an R and see. You will need v = r*ω, too.

    You energy approach looks good. No doubt it could also be done with force, acceleration, etc.
     
  4. Nov 19, 2011 #3

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

  5. Nov 19, 2011 #4
    I think I figured it out. Thanks!
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Hollow sphere rolling down a slope
Loading...