# Sphere rolling up a ramp No mass given

1. Aug 19, 2011

### mightymango

Sphere rolling up a ramp.. No mass given!!

1. The problem statement, all variables and given/known data

A solid sphere of radius 20cm, has a velocity of 5.0m/s and is moving on a surface with just enough friction to allow it to spin. It rolls up an incline of 30 degrees. Calculate the distance rolled before it comes to rest on the incline.

2. Relevant equations

PE + KE = PE
mgh + .5mv^2 = mgh

3. The attempt at a solution

I cancel out m, and plug in: (9.81)(0) + (1/2)(5.0)^2 = (9.81)(h). h is 1.27, so I use trig to find the length of ramp, which is 2.54 m.
However, I feel like I'm missing something crucial in this answer, and none of the choices match.

2. Aug 19, 2011

### PeterO

Re: Sphere rolling up a ramp.. No mass given!!

Are you accounting for the the fact this rather large sphere is spinning?

3. Aug 19, 2011

### rock.freak667

Re: Sphere rolling up a ramp.. No mass given!!

Your KE would be split into rotational KE + translational KE such that:

KE = ½Iω2+ ½mv2 and you know that v=rω

4. Aug 19, 2011

### mightymango

Re: Sphere rolling up a ramp.. No mass given!!

Ok. So I accounted for the spin of the sphere.

New equation is (1/2)(2/5)mr^2w^2 + (1/2)mv^2 = mgh

m's cancel. I plugged in .2m for r, 5 for v, and 25 for w using v=rw. After isolating h, I multiplied by 2 to find the distance on the ramp. However, I'm still not getting the right answer.... Not sure what I'm doing wrong.

5. Aug 19, 2011

### rock.freak667

Re: Sphere rolling up a ramp.. No mass given!!

What value did you get for h and what is the given answer?