# Two Problems on Rotation of a Rigid Body

1. Dec 5, 2006

### mst3kjunkie

the first
and the second:

2. Dec 5, 2006

5.0 m/s cannot be angular velocity, look at the units. It is the translatoral velocity of the sphere's center of mass, I assume.

3. Dec 5, 2006

### mst3kjunkie

that was a mistake on my part. I meant to put velocity, not angular velocity.

4. Dec 5, 2006

Ok, now all you have to do is use energy conservation. Note only that the sphere has translatoral and rotational kinetic energy.

5. Dec 5, 2006

### mst3kjunkie

I'm a bit unsure as to how to set up the formula, still.

6. Dec 5, 2006

Do you know how to use conservation of energy? The kinetic energy (translatoral + rotational) of the sphere must equal the potential energy of the sphere at the highest point on the incline (since the sphere's kinetic energy equals zero at that point).

7. Dec 5, 2006

### mst3kjunkie

I've used Conservation of Energy before, but I haven't encountered the translatoral (at least the term) or rotational energy formulas yet.

8. Dec 5, 2006

$$E_{K,T}=\frac{1}{2}mv^2$$, and
$$E_{K,R}=\frac{1}{2}I \omega^2$$.

9. Dec 5, 2006

### mst3kjunkie

okay, now I"ve gotten it to

(25/2)m+(1/3)mr^2(omega)^2 = 9.8mh

am I on the right track?

10. Dec 5, 2006