- #1

hyddro

- 74

- 2

**Hi guys so this is my first time posting a question on this amazing forum, i hope i am doing this right since i read that no one will help me if i am missing something. Anyways, i am dealing with a physics problem that it driving me crazy (mainly because my teacher does not explain anything!) Here is the problem.**

1. Homework Statement

1. Homework Statement

An 7.50-cm-diameter, 320 g sphere is released from rest at the top of a 1.90-m-long, 20.0 incline. It rolls, without slipping, to the bottom.

b. What fraction of its kinetic energy is rotational?

So the known data is:

mass= 0.0320 kg

radius= 0.0375 m

delta x= 1.90m

wi = 0

vf = 3.02 m/s

wf = 80.5 rad/s

Find ratio between rotational and kinectic energies.

## Homework Equations

Kroll = 1/2 (I* w^2) + 1/2(M)(vf)^2 = Krot + Kcm

## The Attempt at a Solution

ok so from part A of the problem i found the velocity at the bottom of the incline to be 3.02 m/s, then i found the final angular velocity. With that all i thought i had to do was plug the data into the previous equation and get an answer:

Since moment of inertia of a cylinder is 2/5MR^2

Kroll = 1/2 (2/5 ) (0.032kg)(0.0375m)^2 ( 80.5 rad/s)^2 + 1/2 ( 0.032 kg)(3.02 m/s)^2

I am getting 0.204 for the Kroll and for the Krot i am getting 0.06... when i divide 0.06/0.204 i get 0.3 which is not the answer :( i have no idea what am i doing wrong! please help me, this homework was due 2 days ago, i am just doing it to understand the concept no for the points, so i would really appreciate your help, wonderful people, thanks!