# Homework Help: Race between different shapes

1. Feb 19, 2013

### robertmatthew

1. The problem statement, all variables and given/known data
Three uniform objects: a ring, a disk, and a sphere all have identical masses and radii. They are released simultaneously from the top of a ramp 3.80 meters in LENGTH. If the ramp is inclined at θ= 17.0°, use conservation of energy to calculate the linear speed of the ring, disk and sphere.

2. Relevant equations
Ei=Ef
Iring = mr2
Idisk = (mr2)/2
Isphere = (2mr2)/5

3. The attempt at a solution
Ui + Ki = Uf + Kf
mgh = (1/2)Iω2f + (1/)mv2f <--initial K and final U are zero

then substituting I for Iring
mgh = (1/2)((mr2)(vf)/(r)) + (mv2f)
masses cancel, pulled out 1/2
gh = (1/2)(rvf + v2f)

But that's as far as I can get before I can't understand it.

2. Feb 19, 2013

### TSny

Note that ωf is squared.

3. Feb 20, 2013

### robertmatthew

I always end up asking questions on here because of stupid mistakes like that, haha. That made much more sense, with the radii canceling out. Thanks so much.