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!

Homework Help: Sign in Conservation of Angular Momentum Problem

  1. Jan 28, 2008 #1
    1. The problem statement, all variables and given/known data
    A girl of mass M stands on the rim of a frictionless merry-go-round of radius R and rotational inertia I that is not moving. She throws a rock of mass m horizontally in a direction that is tangent to the outer edge of the merry-go-round. The speed of the rock, relative to the ground, is v. Afterward what are (a) the angular speed of the merry-go-round and (b) the linear speed of the girl?

    2. Relevant equations
    L=M(R x V)

    3. The attempt at a solution
    when setting up the conservation of linear momentum I get
    (I+MR^2)w + mRvsin(90) = 0
    although I know I will only get the correct answer by changing the addition sign to a subtraction sign, but still, by the thumb-method the product of r and v should be positive, not negative..so why do I have to make it negative?
  2. jcsd
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Can you offer guidance or do you also need help?
Draft saved Draft deleted